Stop using `six` in Spack (#33905)

Since we dropped support for Python 2.7, there's no need
so use `six` anymore. We still need to vendor it until
we update our vendored dependencies.

83 files changed, 329 insertions, 618 deletions

diff --git a/lib/spack/external/ctest_log_parser.py b/lib/spack/external/ctest_log_parser.py
index d1c8db16c8..0bb31e01b1 100644
--- a/lib/spack/external/ctest_log_parser.py
+++ b/lib/spack/external/ctest_log_parser.py
@@ -71,13 +71,12 @@ from __future__ import division
 import re
 import math
 import multiprocessing
+import io
 import sys
 import threading
 import time
 from contextlib import contextmanager
 
-from six import StringIO
-from six import string_types
 
 _error_matches = [
     "^FAIL: ",
@@ -246,7 +245,7 @@ class LogEvent(object):
 
     def __str__(self):
         """Returns event lines and context."""
-        out = StringIO()
+        out = io.StringIO()
         for i in range(self.start, self.end):
             if i == self.line_no:
                 out.write('  >> %-6d%s' % (i, self[i]))
@@ -386,7 +385,7 @@ class CTestLogParser(object):
             (tuple): two lists containing ``BuildError`` and
                 ``BuildWarning`` objects.
         """
-        if isinstance(stream, string_types):
+        if isinstance(stream, str):
             with open(stream) as f:
                 return self.parse(f, context, jobs)
 
diff --git a/lib/spack/llnl/util/argparsewriter.py b/lib/spack/llnl/util/argparsewriter.py
index a8db508c2f..ad5bf3e83d 100644
--- a/lib/spack/llnl/util/argparsewriter.py
+++ b/lib/spack/llnl/util/argparsewriter.py
@@ -7,11 +7,10 @@ from __future__ import print_function
 
 import argparse
 import errno
+import io
 import re
 import sys
 
-from six import StringIO
-
 
 class Command(object):
     """Parsed representation of a command from argparse.
@@ -181,7 +180,7 @@ class ArgparseRstWriter(ArgparseWriter):
         self.rst_levels = rst_levels
 
     def format(self, cmd):
-        string = StringIO()
+        string = io.StringIO()
         string.write(self.begin_command(cmd.prog))
 
         if cmd.description:
diff --git a/lib/spack/llnl/util/filesystem.py b/lib/spack/llnl/util/filesystem.py
index 30ecc1ebc8..db83cea6fc 100644
--- a/lib/spack/llnl/util/filesystem.py
+++ b/lib/spack/llnl/util/filesystem.py
@@ -18,8 +18,6 @@ import tempfile
 from contextlib import contextmanager
 from sys import platform as _platform
 
-import six
-
 from llnl.util import tty
 from llnl.util.lang import dedupe, memoized
 from llnl.util.symlink import islink, symlink
@@ -520,7 +518,7 @@ def chgrp(path, group, follow_symlinks=True):
     if is_windows:
         raise OSError("Function 'chgrp' is not supported on Windows")
 
-    if isinstance(group, six.string_types):
+    if isinstance(group, str):
         gid = grp.getgrnam(group).gr_gid
     else:
         gid = group
@@ -1017,7 +1015,7 @@ def open_if_filename(str_or_file, mode="r"):
 
     If it's a file object, just yields the file object.
     """
-    if isinstance(str_or_file, six.string_types):
+    if isinstance(str_or_file, str):
         with open(str_or_file, mode) as f:
             yield f
     else:
@@ -1602,7 +1600,7 @@ def find(root, files, recursive=True):
     Returns:
         list: The files that have been found
     """
-    if isinstance(files, six.string_types):
+    if isinstance(files, str):
         files = [files]
 
     if recursive:
@@ -1666,7 +1664,7 @@ class FileList(collections.abc.Sequence):
     """
 
     def __init__(self, files):
-        if isinstance(files, six.string_types):
+        if isinstance(files, str):
             files = [files]
 
         self.files = list(dedupe(files))
@@ -1762,7 +1760,7 @@ class HeaderList(FileList):
     def directories(self, value):
         value = value or []
         # Accept a single directory as input
-        if isinstance(value, six.string_types):
+        if isinstance(value, str):
             value = [value]
 
         self._directories = [path_to_os_path(os.path.normpath(x))[0] for x in value]
@@ -1898,7 +1896,7 @@ def find_headers(headers, root, recursive=False):
     Returns:
         HeaderList: The headers that have been found
     """
-    if isinstance(headers, six.string_types):
+    if isinstance(headers, str):
         headers = [headers]
     elif not isinstance(headers, collections.abc.Sequence):
         message = "{0} expects a string or sequence of strings as the "
@@ -2064,7 +2062,7 @@ def find_system_libraries(libraries, shared=True):
     Returns:
         LibraryList: The libraries that have been found
     """
-    if isinstance(libraries, six.string_types):
+    if isinstance(libraries, str):
         libraries = [libraries]
     elif not isinstance(libraries, collections.abc.Sequence):
         message = "{0} expects a string or sequence of strings as the "
@@ -2121,7 +2119,7 @@ def find_libraries(libraries, root, shared=True, recursive=False, runtime=True):
     Returns:
         LibraryList: The libraries that have been found
     """
-    if isinstance(libraries, six.string_types):
+    if isinstance(libraries, str):
         libraries = [libraries]
     elif not isinstance(libraries, collections.abc.Sequence):
         message = "{0} expects a string or sequence of strings as the "
diff --git a/lib/spack/llnl/util/lang.py b/lib/spack/llnl/util/lang.py
index d8f3cc9b9b..6deb224d70 100644
--- a/lib/spack/llnl/util/lang.py
+++ b/lib/spack/llnl/util/lang.py
@@ -17,9 +17,6 @@ import traceback
 from datetime import datetime, timedelta
 from typing import Any, Callable, Iterable, List, Tuple
 
-import six
-from six import string_types
-
 # Ignore emacs backups when listing modules
 ignore_modules = [r"^\.#", "~$"]
 
@@ -200,14 +197,9 @@ def memoized(func):
             return ret
         except TypeError as e:
             # TypeError is raised when indexing into a dict if the key is unhashable.
-            raise six.raise_from(
-                UnhashableArguments(
-                    "args + kwargs '{}' was not hashable for function '{}'".format(
-                        key, func.__name__
-                    ),
-                ),
-                e,
-            )
+            raise UnhashableArguments(
+                "args + kwargs '{}' was not hashable for function '{}'".format(key, func.__name__),
+            ) from e
 
     return _memoized_function
 
@@ -574,7 +566,7 @@ def match_predicate(*args):
 
     def match(string):
         for arg in args:
-            if isinstance(arg, string_types):
+            if isinstance(arg, str):
                 if re.search(arg, string):
                     return True
             elif isinstance(arg, list) or isinstance(arg, tuple):
diff --git a/lib/spack/llnl/util/tty/__init__.py b/lib/spack/llnl/util/tty/__init__.py
index 7c86411dbe..4b289438fa 100644
--- a/lib/spack/llnl/util/tty/__init__.py
+++ b/lib/spack/llnl/util/tty/__init__.py
@@ -6,6 +6,7 @@
 from __future__ import unicode_literals
 
 import contextlib
+import io
 import os
 import struct
 import sys
@@ -14,10 +15,6 @@ import traceback
 from datetime import datetime
 from sys import platform as _platform
 
-import six
-from six import StringIO
-from six.moves import input
-
 if _platform != "win32":
     import fcntl
     import termios
@@ -183,7 +180,7 @@ def msg(message, *args, **kwargs):
     else:
         cwrite("@*b{%s==>} %s%s" % (st_text, get_timestamp(), cescape(_output_filter(message))))
     for arg in args:
-        print(indent + _output_filter(six.text_type(arg)))
+        print(indent + _output_filter(str(arg)))
 
 
 def info(message, *args, **kwargs):
@@ -201,13 +198,13 @@ def info(message, *args, **kwargs):
         st_text = process_stacktrace(st_countback)
     cprint(
         "@%s{%s==>} %s%s"
-        % (format, st_text, get_timestamp(), cescape(_output_filter(six.text_type(message)))),
+        % (format, st_text, get_timestamp(), cescape(_output_filter(str(message)))),
         stream=stream,
     )
     for arg in args:
         if wrap:
             lines = textwrap.wrap(
-                _output_filter(six.text_type(arg)),
+                _output_filter(str(arg)),
                 initial_indent=indent,
                 subsequent_indent=indent,
                 break_long_words=break_long_words,
@@ -215,7 +212,7 @@ def info(message, *args, **kwargs):
             for line in lines:
                 stream.write(line + "\n")
         else:
-            stream.write(indent + _output_filter(six.text_type(arg)) + "\n")
+            stream.write(indent + _output_filter(str(arg)) + "\n")
 
 
 def verbose(message, *args, **kwargs):
@@ -238,7 +235,7 @@ def error(message, *args, **kwargs):
 
     kwargs.setdefault("format", "*r")
     kwargs.setdefault("stream", sys.stderr)
-    info("Error: " + six.text_type(message), *args, **kwargs)
+    info("Error: " + str(message), *args, **kwargs)
 
 
 def warn(message, *args, **kwargs):
@@ -247,7 +244,7 @@ def warn(message, *args, **kwargs):
 
     kwargs.setdefault("format", "*Y")
     kwargs.setdefault("stream", sys.stderr)
-    info("Warning: " + six.text_type(message), *args, **kwargs)
+    info("Warning: " + str(message), *args, **kwargs)
 
 
 def die(message, *args, **kwargs):
@@ -271,7 +268,7 @@ def get_number(prompt, **kwargs):
     while number is None:
         msg(prompt, newline=False)
         ans = input()
-        if ans == six.text_type(abort):
+        if ans == str(abort):
             return None
 
         if ans:
@@ -336,11 +333,11 @@ def hline(label=None, **kwargs):
         cols -= 2
     cols = min(max_width, cols)
 
-    label = six.text_type(label)
+    label = str(label)
     prefix = char * 2 + " "
     suffix = " " + (cols - len(prefix) - clen(label)) * char
 
-    out = StringIO()
+    out = io.StringIO()
     out.write(prefix)
     out.write(label)
     out.write(suffix)
diff --git a/lib/spack/llnl/util/tty/colify.py b/lib/spack/llnl/util/tty/colify.py
index 73c1daf0d5..4520aad38f 100644
--- a/lib/spack/llnl/util/tty/colify.py
+++ b/lib/spack/llnl/util/tty/colify.py
@@ -8,11 +8,10 @@ Routines for printing columnar output.  See ``colify()`` for more information.
 """
 from __future__ import division, unicode_literals
 
+import io
 import os
 import sys
 
-from six import StringIO, text_type
-
 from llnl.util.tty import terminal_size
 from llnl.util.tty.color import cextra, clen
 
@@ -134,7 +133,7 @@ def colify(elts, **options):
         )
 
     # elts needs to be an array of strings so we can count the elements
-    elts = [text_type(elt) for elt in elts]
+    elts = [str(elt) for elt in elts]
     if not elts:
         return (0, ())
 
@@ -232,7 +231,7 @@ def colify_table(table, **options):
 def colified(elts, **options):
     """Invokes the ``colify()`` function but returns the result as a string
     instead of writing it to an output string."""
-    sio = StringIO()
+    sio = io.StringIO()
     options["output"] = sio
     colify(elts, **options)
     return sio.getvalue()
diff --git a/lib/spack/llnl/util/tty/color.py b/lib/spack/llnl/util/tty/color.py
index ad6862fc28..83e8316914 100644
--- a/lib/spack/llnl/util/tty/color.py
+++ b/lib/spack/llnl/util/tty/color.py
@@ -65,8 +65,6 @@ import re
 import sys
 from contextlib import contextmanager
 
-import six
-
 
 class ColorParseError(Exception):
     """Raised when a color format fails to parse."""
@@ -259,7 +257,7 @@ def cescape(string):
     Returns:
         (str): the string with color codes escaped
     """
-    string = six.text_type(string)
+    string = str(string)
     string = string.replace("@", "@@")
     string = string.replace("}", "}}")
     return string
diff --git a/lib/spack/llnl/util/tty/log.py b/lib/spack/llnl/util/tty/log.py
index 2d6609c390..0b79dd01ac 100644
--- a/lib/spack/llnl/util/tty/log.py
+++ b/lib/spack/llnl/util/tty/log.py
@@ -24,8 +24,6 @@ from threading import Thread
 from types import ModuleType  # novm
 from typing import Optional  # novm
 
-from six import StringIO, string_types
-
 import llnl.util.tty as tty
 
 termios = None  # type: Optional[ModuleType]
@@ -308,7 +306,7 @@ class FileWrapper(object):
 
         self.file_like = file_like
 
-        if isinstance(file_like, string_types):
+        if isinstance(file_like, str):
             self.open = True
         elif _file_descriptors_work(file_like):
             self.open = False
@@ -324,7 +322,7 @@ class FileWrapper(object):
             if self.file_like:
                 self.file = open(self.file_like, "w", encoding="utf-8")
             else:
-                self.file = StringIO()
+                self.file = io.StringIO()
             return self.file
         else:
             # We were handed an already-open file object. In this case we also
@@ -787,7 +785,7 @@ class winlog(object):
             raise RuntimeError("file argument must be set by __init__ ")
 
         # Open both write and reading on logfile
-        if type(self.logfile) == StringIO:
+        if type(self.logfile) == io.StringIO:
             self._ioflag = True
             # cannot have two streams on tempfile, so we must make our own
             sys.stdout = self.logfile
@@ -1013,7 +1011,7 @@ def _writer_daemon(
 
     finally:
         # send written data back to parent if we used a StringIO
-        if isinstance(log_file, StringIO):
+        if isinstance(log_file, io.StringIO):
             control_pipe.send(log_file.getvalue())
         log_file_wrapper.close()
         close_connection_and_file(read_multiprocess_fd, in_pipe)
diff --git a/lib/spack/spack/audit.py b/lib/spack/spack/audit.py
index 5187961930..4bc85dac46 100644
--- a/lib/spack/spack/audit.py
+++ b/lib/spack/spack/audit.py
@@ -42,8 +42,7 @@ import inspect
 import itertools
 import pickle
 import re
-
-from six.moves.urllib.request import urlopen
+from urllib.request import urlopen
 
 import llnl.util.lang
 
diff --git a/lib/spack/spack/binary_distribution.py b/lib/spack/spack/binary_distribution.py
index 1e9843c473..4fbf6e5ec3 100644
--- a/lib/spack/spack/binary_distribution.py
+++ b/lib/spack/spack/binary_distribution.py
@@ -17,9 +17,9 @@ import time
 import traceback
 import warnings
 from contextlib import closing
+from urllib.error import HTTPError, URLError
 
 import ruamel.yaml as yaml
-from six.moves.urllib.error import HTTPError, URLError
 
 import llnl.util.filesystem as fsys
 import llnl.util.lang
diff --git a/lib/spack/spack/bootstrap.py b/lib/spack/spack/bootstrap.py
index 1715eeaafd..e92a1fb6a1 100644
--- a/lib/spack/spack/bootstrap.py
+++ b/lib/spack/spack/bootstrap.py
@@ -17,8 +17,6 @@ import sys
 import sysconfig
 import uuid
 
-import six
-
 import archspec.cpu
 
 import llnl.util.filesystem as fs
@@ -78,7 +76,7 @@ def _try_import_from_store(module, query_spec, query_info=None):
             command found and the concrete spec providing it
     """
     # If it is a string assume it's one of the root specs by this module
-    if isinstance(query_spec, six.string_types):
+    if isinstance(query_spec, str):
         # We have to run as part of this python interpreter
         query_spec += " ^" + spec_for_current_python()
 
@@ -923,7 +921,7 @@ def _missing(name, purpose, system_only=True):
 
 def _required_system_executable(exes, msg):
     """Search for an executable is the system path only."""
-    if isinstance(exes, six.string_types):
+    if isinstance(exes, str):
         exes = (exes,)
     if spack.util.executable.which_string(*exes):
         return True, None
@@ -941,7 +939,7 @@ def _required_python_module(module, query_spec, msg):
 
 def _required_executable(exes, query_spec, msg):
     """Search for an executable in the system path or in the bootstrap store."""
-    if isinstance(exes, six.string_types):
+    if isinstance(exes, str):
         exes = (exes,)
     if spack.util.executable.which_string(*exes) or _executables_in_store(exes, query_spec):
         return True, None
diff --git a/lib/spack/spack/build_environment.py b/lib/spack/spack/build_environment.py
index f1a1ce3dc8..5b9120d2ff 100644
--- a/lib/spack/spack/build_environment.py
+++ b/lib/spack/spack/build_environment.py
@@ -33,6 +33,7 @@ Skimming this module is a nice way to get acquainted with the types of
 calls you can make from within the install() function.
 """
 import inspect
+import io
 import multiprocessing
 import os
 import re
@@ -41,8 +42,6 @@ import sys
 import traceback
 import types
 
-from six import StringIO
-
 import llnl.util.tty as tty
 from llnl.util.filesystem import install, install_tree, mkdirp
 from llnl.util.lang import dedupe
@@ -1352,7 +1351,7 @@ class ChildError(InstallError):
 
     @property
     def long_message(self):
-        out = StringIO()
+        out = io.StringIO()
         out.write(self._long_message if self._long_message else "")
 
         have_log = self.log_name and os.path.exists(self.log_name)
diff --git a/lib/spack/spack/build_systems/_checks.py b/lib/spack/spack/build_systems/_checks.py
index 73d5bbdb93..658362902b 100644
--- a/lib/spack/spack/build_systems/_checks.py
+++ b/lib/spack/spack/build_systems/_checks.py
@@ -4,8 +4,6 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import os
 
-import six
-
 import llnl.util.lang
 
 import spack.builder
@@ -26,7 +24,7 @@ def sanity_check_prefix(builder):
     pkg = builder.pkg
 
     def check_paths(path_list, filetype, predicate):
-        if isinstance(path_list, six.string_types):
+        if isinstance(path_list, str):
             path_list = [path_list]
 
         for path in path_list:
diff --git a/lib/spack/spack/build_systems/cmake.py b/lib/spack/spack/build_systems/cmake.py
index 9456726d3e..6210db9d4a 100644
--- a/lib/spack/spack/build_systems/cmake.py
+++ b/lib/spack/spack/build_systems/cmake.py
@@ -10,8 +10,6 @@ import re
 import sys
 from typing import List, Tuple
 
-import six
-
 import llnl.util.filesystem as fs
 
 import spack.build_environment
@@ -302,9 +300,7 @@ class CMakeBuilder(BaseBuilder):
             value = "ON" if value else "OFF"
         else:
             kind = "STRING"
-            if isinstance(value, collections.abc.Sequence) and not isinstance(
-                value, six.string_types
-            ):
+            if isinstance(value, collections.abc.Sequence) and not isinstance(value, str):
                 value = ";".join(str(v) for v in value)
             else:
                 value = str(value)
diff --git a/lib/spack/spack/builder.py b/lib/spack/spack/builder.py
index 063a7f0611..4308206d52 100644
--- a/lib/spack/spack/builder.py
+++ b/lib/spack/spack/builder.py
@@ -9,8 +9,6 @@ import functools
 import inspect
 from typing import List, Optional, Tuple
 
-import six
-
 import spack.build_environment
 
 #: Builder classes, as registered by the "builder" decorator
@@ -167,7 +165,7 @@ def _create(pkg):
             property(forward_property_to_getattr(attribute_name)),
         )
 
-    class Adapter(six.with_metaclass(_PackageAdapterMeta, base_cls)):
+    class Adapter(base_cls, metaclass=_PackageAdapterMeta):
         def __init__(self, pkg):
             # Deal with custom phases in packages here
             if hasattr(pkg, "phases"):
@@ -456,7 +454,7 @@ class InstallationPhase(object):
         return copy.deepcopy(self)
 
 
-class Builder(six.with_metaclass(BuilderMeta, collections.abc.Sequence)):
+class Builder(collections.abc.Sequence, metaclass=BuilderMeta):
     """A builder is a class that, given a package object (i.e. associated with
     concrete spec), knows how to install it.
 
diff --git a/lib/spack/spack/ci.py b/lib/spack/spack/ci.py
index d6113c0dc9..522c7d8b78 100644
--- a/lib/spack/spack/ci.py
+++ b/lib/spack/spack/ci.py
@@ -16,11 +16,9 @@ import sys
 import tempfile
 import time
 import zipfile
-
-from six import iteritems, string_types
-from six.moves.urllib.error import HTTPError, URLError
-from six.moves.urllib.parse import urlencode
-from six.moves.urllib.request import HTTPHandler, Request, build_opener
+from urllib.error import HTTPError, URLError
+from urllib.parse import urlencode
+from urllib.request import HTTPHandler, Request, build_opener
 
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
@@ -216,7 +214,7 @@ def stage_spec_jobs(specs, check_index_only=False, mirrors_to_check=None):
     def _remove_satisfied_deps(deps, satisfied_list):
         new_deps = {}
 
-        for key, value in iteritems(deps):
+        for key, value in deps.items():
             new_value = set([v for v in value if v not in satisfied_list])
             if new_value:
                 new_deps[key] = new_value
@@ -1970,7 +1968,7 @@ def process_command(name, commands, repro_dir):
     """
     tty.debug("spack {0} arguments: {1}".format(name, commands))
 
-    if len(commands) == 0 or isinstance(commands[0], string_types):
+    if len(commands) == 0 or isinstance(commands[0], str):
         commands = [commands]
 
     # Create a string [command 1] && [command 2] && ... && [command n] with commands
diff --git a/lib/spack/spack/cmd/__init__.py b/lib/spack/spack/cmd/__init__.py
index ef02e8f9e4..f847bf9be4 100644
--- a/lib/spack/spack/cmd/__init__.py
+++ b/lib/spack/spack/cmd/__init__.py
@@ -14,7 +14,6 @@ from textwrap import dedent
 from typing import List, Tuple
 
 import ruamel.yaml as yaml
-import six
 from ruamel.yaml.error import MarkedYAMLError
 
 import llnl.util.tty as tty
@@ -217,7 +216,7 @@ def parse_specs(args, **kwargs):
     tests = kwargs.get("tests", False)
 
     sargs = args
-    if not isinstance(args, six.string_types):
+    if not isinstance(args, str):
         sargs = " ".join(args)
     unquoted_flags = _UnquotedFlags.extract(sargs)
 
diff --git a/lib/spack/spack/cmd/compiler.py b/lib/spack/spack/cmd/compiler.py
index 75c5f05d0f..2929db3ad6 100644
--- a/lib/spack/spack/cmd/compiler.py
+++ b/lib/spack/spack/cmd/compiler.py
@@ -8,8 +8,6 @@ from __future__ import print_function
 import argparse
 import sys
 
-from six import iteritems
-
 import llnl.util.tty as tty
 from llnl.util.lang import index_by
 from llnl.util.tty.colify import colify
@@ -138,13 +136,13 @@ def compiler_info(args):
                 print("\t\t%s = %s" % (cpath, getattr(c, cpath, None)))
             if c.flags:
                 print("\tflags:")
-                for flag, flag_value in iteritems(c.flags):
+                for flag, flag_value in c.flags.items():
                     print("\t\t%s = %s" % (flag, flag_value))
             if len(c.environment) != 0:
                 if len(c.environment.get("set", {})) != 0:
                     print("\tenvironment:")
                     print("\t    set:")
-                    for key, value in iteritems(c.environment["set"]):
+                    for key, value in c.environment["set"].items():
                         print("\t        %s = %s" % (key, value))
             if c.extra_rpaths:
                 print("\tExtra rpaths:")
diff --git a/lib/spack/spack/cmd/env.py b/lib/spack/spack/cmd/env.py
index 558b6bead4..5510c7443a 100644
--- a/lib/spack/spack/cmd/env.py
+++ b/lib/spack/spack/cmd/env.py
@@ -4,13 +4,12 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 import argparse
+import io
 import os
 import shutil
 import sys
 import tempfile
 
-import six
-
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
 from llnl.util.tty.colify import colify
@@ -737,7 +736,7 @@ def env_depfile(args):
         [get_install_deps_target(h) for h, _, _, _ in make_targets.adjacency_list]
     )
 
-    buf = six.StringIO()
+    buf = io.StringIO()
 
     template = spack.tengine.make_environment().get_template(os.path.join("depfile", "Makefile"))
 
diff --git a/lib/spack/spack/cmd/info.py b/lib/spack/spack/cmd/info.py
index 6a16a153ea..5076ff9261 100644
--- a/lib/spack/spack/cmd/info.py
+++ b/lib/spack/spack/cmd/info.py
@@ -7,8 +7,7 @@ from __future__ import print_function
 
 import inspect
 import textwrap
-
-from six.moves import zip_longest
+from itertools import zip_longest
 
 import llnl.util.tty as tty
 import llnl.util.tty.color as color
diff --git a/lib/spack/spack/cmd/providers.py b/lib/spack/spack/cmd/providers.py
index 2c1b146f6a..73a960a708 100644
--- a/lib/spack/spack/cmd/providers.py
+++ b/lib/spack/spack/cmd/providers.py
@@ -3,10 +3,9 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import io
 import sys
 
-import six
-
 import llnl.util.tty.colify as colify
 
 import spack.cmd
@@ -29,7 +28,7 @@ def setup_parser(subparser):
 def providers(parser, args):
     valid_virtuals = sorted(spack.repo.path.provider_index.providers.keys())
 
-    buffer = six.StringIO()
+    buffer = io.StringIO()
     isatty = sys.stdout.isatty()
     if isatty:
         buffer.write("Virtual packages:\n")
diff --git a/lib/spack/spack/cmd/tags.py b/lib/spack/spack/cmd/tags.py
index 6ba9717784..b720055a15 100644
--- a/lib/spack/spack/cmd/tags.py
+++ b/lib/spack/spack/cmd/tags.py
@@ -2,11 +2,9 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
+import io
 import sys
 
-import six
-
 import llnl.util.tty as tty
 import llnl.util.tty.colify as colify
 
@@ -20,7 +18,7 @@ level = "long"
 
 
 def report_tags(category, tags):
-    buffer = six.StringIO()
+    buffer = io.StringIO()
     isatty = sys.stdout.isatty()
 
     if isatty:
@@ -88,7 +86,7 @@ def tags(parser, args):
         return
 
     # Report packages associated with tags
-    buffer = six.StringIO()
+    buffer = io.StringIO()
     isatty = sys.stdout.isatty()
 
     tags = args.tag if args.tag else available_tags
diff --git a/lib/spack/spack/cmd/unit_test.py b/lib/spack/spack/cmd/unit_test.py
index d1d0c790f8..55c8b17f9c 100644
--- a/lib/spack/spack/cmd/unit_test.py
+++ b/lib/spack/spack/cmd/unit_test.py
@@ -7,6 +7,7 @@ from __future__ import division, print_function
 
 import argparse
 import collections
+import io
 import os.path
 import re
 import sys
@@ -16,8 +17,6 @@ try:
 except ImportError:
     pytest = None  # type: ignore
 
-from six import StringIO
-
 import llnl.util.filesystem
 import llnl.util.tty.color as color
 from llnl.util.tty.colify import colify
@@ -126,7 +125,7 @@ def do_list(args, extra_args):
 
     old_output = sys.stdout
     try:
-        sys.stdout = output = StringIO()
+        sys.stdout = output = io.StringIO()
         pytest.main(["--collect-only"] + extra_args)
     finally:
         sys.stdout = old_output
diff --git a/lib/spack/spack/cmd/url.py b/lib/spack/spack/cmd/url.py
index 452bd059da..1c9b5aea53 100644
--- a/lib/spack/spack/cmd/url.py
+++ b/lib/spack/spack/cmd/url.py
@@ -5,10 +5,9 @@
 
 from __future__ import division, print_function
 
+import urllib.parse
 from collections import defaultdict
 
-import six.moves.urllib.parse as urllib_parse
-
 import llnl.util.tty.color as color
 from llnl.util import tty
 
@@ -323,7 +322,7 @@ def url_stats(args):
                     md5_hashes[pkg_name].append(fetcher.url)
 
                 # parse out the URL scheme (https/http/ftp/etc.)
-                urlinfo = urllib_parse.urlparse(fetcher.url)
+                urlinfo = urllib.parse.urlparse(fetcher.url)
                 self.schemes[urlinfo.scheme] += 1
 
                 if urlinfo.scheme == "http":
diff --git a/lib/spack/spack/compilers/__init__.py b/lib/spack/spack/compilers/__init__.py
index e54f8dc96c..b7c8cd2232 100644
--- a/lib/spack/spack/compilers/__init__.py
+++ b/lib/spack/spack/compilers/__init__.py
@@ -12,8 +12,6 @@ import multiprocessing.pool
 import os
 from typing import Dict  # novm
 
-import six
-
 import archspec.cpu
 
 import llnl.util.filesystem as fs
@@ -427,7 +425,7 @@ def compiler_from_dict(items):
         environment,
         extra_rpaths,
         enable_implicit_rpaths=implicit_rpaths,
-        **compiler_flags
+        **compiler_flags,
     )
 
 
@@ -677,18 +675,18 @@ def detect_version(detect_version_args):
 
         try:
             version = callback(path)
-            if version and six.text_type(version).strip() and version != "unknown":
+            if version and str(version).strip() and version != "unknown":
                 value = fn_args._replace(id=compiler_id._replace(version=version))
                 return value, None
 
             error = "Couldn't get version for compiler {0}".format(path)
         except spack.util.executable.ProcessError as e:
-            error = "Couldn't get version for compiler {0}\n".format(path) + six.text_type(e)
+            error = "Couldn't get version for compiler {0}\n".format(path) + str(e)
         except Exception as e:
             # Catching "Exception" here is fine because it just
             # means something went wrong running a candidate executable.
             error = "Error while executing candidate compiler {0}" "\n{1}: {2}".format(
-                path, e.__class__.__name__, six.text_type(e)
+                path, e.__class__.__name__, str(e)
             )
         return None, error
 
diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index e9a3b1d956..c3165d1c9c 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -39,9 +39,7 @@ from contextlib import contextmanager
 from typing import List  # novm
 
 import ruamel.yaml as yaml
-import six
 from ruamel.yaml.error import MarkedYAMLError
-from six import iteritems
 
 import llnl.util.lang
 import llnl.util.tty as tty
@@ -358,7 +356,7 @@ class InternalConfigScope(ConfigScope):
     def _process_dict_keyname_overrides(data):
         """Turn a trailing `:' in a key name into an override attribute."""
         result = {}
-        for sk, sv in iteritems(data):
+        for sk, sv in data.items():
             if sk.endswith(":"):
                 key = syaml.syaml_str(sk[:-1])
                 key.override = True
@@ -973,7 +971,7 @@ def validate(data, schema, filename=None):
             line_number = e.instance.lc.line + 1
         else:
             line_number = None
-        raise six.raise_from(ConfigFormatError(e, data, filename, line_number), e)
+        raise ConfigFormatError(e, data, filename, line_number) from e
     # return the validated data so that we can access the raw data
     # mostly relevant for environments
     return test_data
@@ -1140,7 +1138,7 @@ def merge_yaml(dest, source):
         # come *before* dest in OrderdDicts
         dest_keys = [dk for dk in dest.keys() if dk not in source]
 
-        for sk, sv in iteritems(source):
+        for sk, sv in source.items():
             # always remove the dest items. Python dicts do not overwrite
             # keys on insert, so this ensures that source keys are copied
             # into dest along with mark provenance (i.e., file/line info).
diff --git a/lib/spack/spack/cray_manifest.py b/lib/spack/spack/cray_manifest.py
index 631280c473..66dd33ce7c 100644
--- a/lib/spack/spack/cray_manifest.py
+++ b/lib/spack/spack/cray_manifest.py
@@ -7,7 +7,6 @@ import json
 
 import jsonschema
 import jsonschema.exceptions
-import six
 
 import llnl.util.tty as tty
 
@@ -97,7 +96,7 @@ def spec_from_entry(entry):
                 continue
 
             # Value could be a list (of strings), boolean, or string
-            if isinstance(value, six.string_types):
+            if isinstance(value, str):
                 variant_strs.append("{0}={1}".format(name, value))
             else:
                 try:
@@ -169,10 +168,7 @@ def read(path, apply_updates):
 
         jsonschema.validate(json_data, manifest_schema)
     except (jsonschema.exceptions.ValidationError, decode_exception_type) as e:
-        raise six.raise_from(
-            ManifestValidationError("error parsing manifest JSON:", str(e)),
-            e,
-        )
+        raise ManifestValidationError("error parsing manifest JSON:", str(e)) from e
 
     specs = entries_to_specs(json_data["specs"])
     tty.debug("{0}: {1} specs read from manifest".format(path, str(len(specs))))
diff --git a/lib/spack/spack/database.py b/lib/spack/spack/database.py
index 74e2ec98c3..f74008e8f3 100644
--- a/lib/spack/spack/database.py
+++ b/lib/spack/spack/database.py
@@ -28,8 +28,6 @@ import sys
 import time
 from typing import Dict  # novm
 
-import six
-
 try:
     import uuid
 
@@ -770,10 +768,7 @@ class Database(object):
             with open(filename, "r") as f:
                 fdata = sjson.load(f)
         except Exception as e:
-            raise six.raise_from(
-                CorruptDatabaseError("error parsing database:", str(e)),
-                e,
-            )
+            raise CorruptDatabaseError("error parsing database:", str(e)) from e
 
         if fdata is None:
             return
diff --git a/lib/spack/spack/dependency.py b/lib/spack/spack/dependency.py
index 1b38cd5092..bdf660fd1d 100644
--- a/lib/spack/spack/dependency.py
+++ b/lib/spack/spack/dependency.py
@@ -2,11 +2,7 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-"""Data structures that represent Spack's dependency relationships.
-"""
-from six import string_types
-
+"""Data structures that represent Spack's dependency relationships."""
 import spack.spec
 
 #: The types of dependency relationships that Spack understands.
@@ -48,7 +44,7 @@ def canonical_deptype(deptype):
     if deptype in ("all", all):
         return all_deptypes
 
-    elif isinstance(deptype, string_types):
+    elif isinstance(deptype, str):
         if deptype not in all_deptypes:
             raise ValueError("Invalid dependency type: %s" % deptype)
         return (deptype,)
diff --git a/lib/spack/spack/detection/common.py b/lib/spack/spack/detection/common.py
index b9cd871fc2..8233f47eb8 100644
--- a/lib/spack/spack/detection/common.py
+++ b/lib/spack/spack/detection/common.py
@@ -20,8 +20,6 @@ import os.path
 import re
 import sys
 
-import six
-
 import llnl.util.tty
 
 import spack.config
@@ -115,7 +113,7 @@ def _convert_to_iterable(single_val_or_multiple):
     x = single_val_or_multiple
     if x is None:
         return []
-    elif isinstance(x, six.string_types):
+    elif isinstance(x, str):
         return [x]
     elif isinstance(x, spack.spec.Spec):
         # Specs are iterable, but a single spec should be converted to a list
diff --git a/lib/spack/spack/directives.py b/lib/spack/spack/directives.py
index 412e34bf05..cfaeeec9ab 100644
--- a/lib/spack/spack/directives.py
+++ b/lib/spack/spack/directives.py
@@ -34,8 +34,6 @@ import os.path
 import re
 from typing import List, Set  # novm
 
-import six
-
 import llnl.util.lang
 import llnl.util.tty.color
 
@@ -234,7 +232,7 @@ class DirectiveMeta(type):
         """
         global directive_names
 
-        if isinstance(dicts, six.string_types):
+        if isinstance(dicts, str):
             dicts = (dicts,)
 
         if not isinstance(dicts, collections.abc.Sequence):
@@ -391,7 +389,7 @@ def _depends_on(pkg, spec, when=None, type=default_deptype, patches=None):
         patches = [patches]
 
     # auto-call patch() directive on any strings in patch list
-    patches = [patch(p) if isinstance(p, six.string_types) else p for p in patches]
+    patches = [patch(p) if isinstance(p, str) else p for p in patches]
     assert all(callable(p) for p in patches)
 
     # this is where we actually add the dependency to this package
diff --git a/lib/spack/spack/directory_layout.py b/lib/spack/spack/directory_layout.py
index 607f8bc39d..34ebb7d93d 100644
--- a/lib/spack/spack/directory_layout.py
+++ b/lib/spack/spack/directory_layout.py
@@ -12,8 +12,6 @@ import shutil
 import sys
 from contextlib import contextmanager
 
-import six
-
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
 
@@ -363,12 +361,12 @@ class DirectoryLayout(object):
                     os.unlink(path)
                     os.remove(metapath)
                 except OSError as e:
-                    raise six.raise_from(RemoveFailedError(spec, path, e), e)
+                    raise RemoveFailedError(spec, path, e) from e
         elif os.path.exists(path):
             try:
                 shutil.rmtree(path, **kwargs)
             except OSError as e:
-                raise six.raise_from(RemoveFailedError(spec, path, e), e)
+                raise RemoveFailedError(spec, path, e) from e
 
         path = os.path.dirname(path)
         while path != self.root:
diff --git a/lib/spack/spack/environment/environment.py b/lib/spack/spack/environment/environment.py
index f0598e5a83..6ac6908ff3 100644
--- a/lib/spack/spack/environment/environment.py
+++ b/lib/spack/spack/environment/environment.py
@@ -13,7 +13,6 @@ import sys
 import time
 
 import ruamel.yaml as yaml
-import six
 
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
@@ -679,7 +678,7 @@ class Environment(object):
             self.views = {}
         elif with_view is True:
             self.views = {default_view_name: ViewDescriptor(self.path, self.view_path_default)}
-        elif isinstance(with_view, six.string_types):
+        elif isinstance(with_view, str):
             self.views = {default_view_name: ViewDescriptor(self.path, with_view)}
         # If with_view is None, then defer to the view settings determined by
         # the manifest file
@@ -776,7 +775,7 @@ class Environment(object):
         # enable_view can be boolean, string, or None
         if enable_view is True or enable_view is None:
             self.views = {default_view_name: ViewDescriptor(self.path, self.view_path_default)}
-        elif isinstance(enable_view, six.string_types):
+        elif isinstance(enable_view, str):
             self.views = {default_view_name: ViewDescriptor(self.path, enable_view)}
         elif enable_view:
             path = self.path
@@ -2096,16 +2095,14 @@ class Environment(object):
                 ayl[name][:] = [
                     s
                     for s in ayl.setdefault(name, [])
-                    if (not isinstance(s, six.string_types))
-                    or s.startswith("$")
-                    or Spec(s) in speclist.specs
+                    if (not isinstance(s, str)) or s.startswith("$") or Spec(s) in speclist.specs
                 ]
 
             # Put the new specs into the first active list from the yaml
             new_specs = [
                 entry
                 for entry in speclist.yaml_list
-                if isinstance(entry, six.string_types)
+                if isinstance(entry, str)
                 and not any(entry in ayl[name] for ayl in active_yaml_lists)
             ]
             list_for_new_specs = active_yaml_lists[0].setdefault(name, [])
@@ -2181,7 +2178,7 @@ def yaml_equivalent(first, second):
     elif isinstance(first, list):
         return isinstance(second, list) and _equiv_list(first, second)
     else:  # it's a string
-        return isinstance(second, six.string_types) and first == second
+        return isinstance(second, str) and first == second
 
 
 def _equiv_list(first, second):
diff --git a/lib/spack/spack/fetch_strategy.py b/lib/spack/spack/fetch_strategy.py
index df993978af..3b908054e3 100644
--- a/lib/spack/spack/fetch_strategy.py
+++ b/lib/spack/spack/fetch_strategy.py
@@ -29,11 +29,9 @@ import os.path
 import re
 import shutil
 import sys
+import urllib.parse
 from typing import List, Optional  # novm
 
-import six
-import six.moves.urllib.parse as urllib_parse
-
 import llnl.util
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
@@ -322,7 +320,7 @@ class URLFetchStrategy(FetchStrategy):
             # This must be skipped on Windows due to URL encoding
             # of ':' characters on filepaths on Windows
             if sys.platform != "win32" and url.startswith("file://"):
-                path = urllib_parse.quote(url[len("file://") :])
+                path = urllib.parse.quote(url[len("file://") :])
                 url = "file://" + path
             urls.append(url)
 
@@ -620,7 +618,7 @@ class VCSFetchStrategy(FetchStrategy):
 
         patterns = kwargs.get("exclude", None)
         if patterns is not None:
-            if isinstance(patterns, six.string_types):
+            if isinstance(patterns, str):
                 patterns = [patterns]
             for p in patterns:
                 tar.add_default_arg("--exclude=%s" % p)
@@ -1607,7 +1605,7 @@ def from_url_scheme(url, *args, **kwargs):
     in the given url."""
 
     url = kwargs.get("url", url)
-    parsed_url = urllib_parse.urlparse(url, scheme="file")
+    parsed_url = urllib.parse.urlparse(url, scheme="file")
 
     scheme_mapping = kwargs.get("scheme_mapping") or {
         "file": "url",
diff --git a/lib/spack/spack/gcs_handler.py b/lib/spack/spack/gcs_handler.py
index 13121be603..4b547a78dc 100644
--- a/lib/spack/spack/gcs_handler.py
+++ b/lib/spack/spack/gcs_handler.py
@@ -2,8 +2,7 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-import six.moves.urllib.response as urllib_response
+import urllib.response
 
 import spack.util.url as url_util
 import spack.util.web as web_util
@@ -21,4 +20,4 @@ def gcs_open(req, *args, **kwargs):
     stream = gcsblob.get_blob_byte_stream()
     headers = gcsblob.get_blob_headers()
 
-    return urllib_response.addinfourl(stream, headers, url)
+    return urllib.response.addinfourl(stream, headers, url)
diff --git a/lib/spack/spack/install_test.py b/lib/spack/spack/install_test.py
index 130dca088a..24764a28c9 100644
--- a/lib/spack/spack/install_test.py
+++ b/lib/spack/spack/install_test.py
@@ -8,8 +8,6 @@ import os
 import re
 import shutil
 
-import six
-
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
 
@@ -434,10 +432,7 @@ class TestSuite(object):
                 test_suite._hash = content_hash
                 return test_suite
         except Exception as e:
-            raise six.raise_from(
-                sjson.SpackJSONError("error parsing JSON TestSuite:", str(e)),
-                e,
-            )
+            raise sjson.SpackJSONError("error parsing JSON TestSuite:", str(e)) from e
 
 
 def _add_msg_to_file(filename, msg):
diff --git a/lib/spack/spack/installer.py b/lib/spack/spack/installer.py
index 252c799304..41860ced19 100644
--- a/lib/spack/spack/installer.py
+++ b/lib/spack/spack/installer.py
@@ -2,7 +2,6 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
 """
 This module encapsulates package installation functionality.
 
@@ -30,6 +29,7 @@ installations of packages in a Spack instance.
 import copy
 import glob
 import heapq
+import io
 import itertools
 import os
 import shutil
@@ -37,8 +37,6 @@ import sys
 import time
 from collections import defaultdict
 
-import six
-
 import llnl.util.filesystem as fs
 import llnl.util.lock as lk
 import llnl.util.tty as tty
@@ -594,7 +592,7 @@ def log(pkg):
 
     # Finally, archive files that are specific to each package
     with fs.working_dir(pkg.stage.path):
-        errors = six.StringIO()
+        errors = io.StringIO()
         target_dir = os.path.join(spack.store.layout.metadata_path(pkg.spec), "archived-files")
 
         for glob_expr in pkg.builder.archive_files:
diff --git a/lib/spack/spack/main.py b/lib/spack/spack/main.py
index 58785d8390..2ef78e07f9 100644
--- a/lib/spack/spack/main.py
+++ b/lib/spack/spack/main.py
@@ -12,6 +12,7 @@ from __future__ import print_function
 
 import argparse
 import inspect
+import io
 import operator
 import os
 import os.path
@@ -23,8 +24,6 @@ import sys
 import traceback
 import warnings
 
-from six import StringIO
-
 import archspec.cpu
 
 import llnl.util.lang
@@ -700,7 +699,7 @@ class SpackCommand(object):
                 prepend + [self.command_name] + list(argv)
             )
 
-            out = StringIO()
+            out = io.StringIO()
             try:
                 with log_output(out):
                     self.returncode = _invoke_command(self.command, self.parser, args, unknown)
diff --git a/lib/spack/spack/mirror.py b/lib/spack/spack/mirror.py
index 41853c39b9..8e914306e0 100644
--- a/lib/spack/spack/mirror.py
+++ b/lib/spack/spack/mirror.py
@@ -19,7 +19,6 @@ import sys
 import traceback
 
 import ruamel.yaml.error as yaml_error
-import six
 
 import llnl.util.tty as tty
 from llnl.util.filesystem import mkdirp
@@ -37,7 +36,7 @@ from spack.version import VersionList
 
 
 def _is_string(url):
-    return isinstance(url, six.string_types)
+    return isinstance(url, str)
 
 
 def _display_mirror_entry(size, name, url, type_=None):
@@ -78,10 +77,7 @@ class Mirror(object):
             data = syaml.load(stream)
             return Mirror.from_dict(data, name)
         except yaml_error.MarkedYAMLError as e:
-            raise six.raise_from(
-                syaml.SpackYAMLError("error parsing YAML mirror:", str(e)),
-                e,
-            )
+            raise syaml.SpackYAMLError("error parsing YAML mirror:", str(e)) from e
 
     @staticmethod
     def from_json(stream, name=None):
@@ -89,10 +85,7 @@ class Mirror(object):
             d = sjson.load(stream)
             return Mirror.from_dict(d, name)
         except Exception as e:
-            raise six.raise_from(
-                sjson.SpackJSONError("error parsing JSON mirror:", str(e)),
-                e,
-            )
+            raise sjson.SpackJSONError("error parsing JSON mirror:", str(e)) from e
 
     def to_dict(self):
         if self._push_url is None:
@@ -102,7 +95,7 @@ class Mirror(object):
 
     @staticmethod
     def from_dict(d, name=None):
-        if isinstance(d, six.string_types):
+        if isinstance(d, str):
             return Mirror(d, name=name)
         else:
             return Mirror(d["fetch"], d["push"], name=name)
@@ -257,10 +250,7 @@ class MirrorCollection(collections.abc.Mapping):
             data = syaml.load(stream)
             return MirrorCollection(data)
         except yaml_error.MarkedYAMLError as e:
-            raise six.raise_from(
-                syaml.SpackYAMLError("error parsing YAML mirror collection:", str(e)),
-                e,
-            )
+            raise syaml.SpackYAMLError("error parsing YAML mirror collection:", str(e)) from e
 
     @staticmethod
     def from_json(stream, name=None):
@@ -268,10 +258,7 @@ class MirrorCollection(collections.abc.Mapping):
             d = sjson.load(stream)
             return MirrorCollection(d)
         except Exception as e:
-            raise six.raise_from(
-                sjson.SpackJSONError("error parsing JSON mirror collection:", str(e)),
-                e,
-            )
+            raise sjson.SpackJSONError("error parsing JSON mirror collection:", str(e)) from e
 
     def to_dict(self, recursive=False):
         return syaml_dict(
diff --git a/lib/spack/spack/package_base.py b/lib/spack/spack/package_base.py
index 957b947f79..81fbe86ee0 100644
--- a/lib/spack/spack/package_base.py
+++ b/lib/spack/spack/package_base.py
@@ -2,7 +2,6 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
 """This is where most of the action happens in Spack.
 
 The spack package class structure is based strongly on Homebrew
@@ -18,6 +17,7 @@ import functools
 import glob
 import hashlib
 import inspect
+import io
 import os
 import re
 import shutil
@@ -29,8 +29,6 @@ import types
 import warnings
 from typing import Any, Callable, Dict, Iterable, List, Optional, Tuple, Type  # novm
 
-import six
-
 import llnl.util.filesystem as fsys
 import llnl.util.tty as tty
 from llnl.util.lang import classproperty, memoized, nullcontext
@@ -130,7 +128,7 @@ def preferred_version(pkg):
     return sorted(pkg.versions, key=key_fn).pop()
 
 
-class WindowsRPathMeta(object):
+class WindowsRPath(object):
     """Collection of functionality surrounding Windows RPATH specific features
 
     This is essentially meaningless for all other platforms
@@ -256,7 +254,7 @@ class DetectablePackageMeta(object):
                         variants = [variants]
 
                     for variant in variants:
-                        if isinstance(variant, six.string_types):
+                        if isinstance(variant, str):
                             variant = (variant, {})
                         variant_str, extra_attributes = variant
                         spec_str = "{0}@{1} {2}".format(cls.name, version_str, variant_str)
@@ -443,7 +441,7 @@ def test_log_pathname(test_stage, spec):
     return os.path.join(test_stage, "test-{0}-out.txt".format(TestSuite.test_pkg_id(spec)))
 
 
-class PackageBase(six.with_metaclass(PackageMeta, WindowsRPathMeta, PackageViewMixin, object)):
+class PackageBase(WindowsRPath, PackageViewMixin, metaclass=PackageMeta):
     """This is the superclass for all spack packages.
 
     ***The Package class***
@@ -1870,7 +1868,7 @@ class PackageBase(six.with_metaclass(PackageMeta, WindowsRPathMeta, PackageViewM
                 be copied to the corresponding location(s) under the install
                 testing directory.
         """
-        paths = [srcs] if isinstance(srcs, six.string_types) else srcs
+        paths = [srcs] if isinstance(srcs, str) else srcs
 
         for path in paths:
             src_path = os.path.join(self.stage.source_path, path)
@@ -2000,7 +1998,7 @@ class PackageBase(six.with_metaclass(PackageMeta, WindowsRPathMeta, PackageViewM
                     print(line.rstrip("\n"))
 
                 if exc_type is spack.util.executable.ProcessError:
-                    out = six.StringIO()
+                    out = io.StringIO()
                     spack.build_environment.write_log_summary(
                         out, "test", self.test_log_file, last=1
                     )
@@ -2022,9 +2020,9 @@ class PackageBase(six.with_metaclass(PackageMeta, WindowsRPathMeta, PackageViewM
                 return False
 
     def _run_test_helper(self, runner, options, expected, status, installed, purpose):
-        status = [status] if isinstance(status, six.integer_types) else status
-        expected = [expected] if isinstance(expected, six.string_types) else expected
-        options = [options] if isinstance(options, six.string_types) else options
+        status = [status] if isinstance(status, int) else status
+        expected = [expected] if isinstance(expected, str) else expected
+        options = [options] if isinstance(options, str) else options
 
         if purpose:
             tty.msg(purpose)
@@ -2365,7 +2363,7 @@ class PackageBase(six.with_metaclass(PackageMeta, WindowsRPathMeta, PackageViewM
 
         doc = re.sub(r"\s+", " ", cls.__doc__)
         lines = textwrap.wrap(doc, 72)
-        results = six.StringIO()
+        results = io.StringIO()
         for line in lines:
             results.write((" " * indent) + line + "\n")
         return results.getvalue()
diff --git a/lib/spack/spack/package_prefs.py b/lib/spack/spack/package_prefs.py
index 48d1ca129d..79beaba492 100644
--- a/lib/spack/spack/package_prefs.py
+++ b/lib/spack/spack/package_prefs.py
@@ -4,8 +4,6 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import stat
 
-from six import string_types
-
 import spack.error
 import spack.repo
 from spack.config import ConfigError
@@ -144,7 +142,7 @@ class PackagePrefs(object):
                 break
 
         # allow variants to be list or string
-        if not isinstance(variants, string_types):
+        if not isinstance(variants, str):
             variants = " ".join(variants)
 
         # Only return variants that are actually supported by the package
diff --git a/lib/spack/spack/parse.py b/lib/spack/spack/parse.py
index 61260bc837..c967dc709d 100644
--- a/lib/spack/spack/parse.py
+++ b/lib/spack/spack/parse.py
@@ -8,8 +8,6 @@ import re
 import shlex
 import sys
 
-from six import string_types
-
 import spack.error
 import spack.util.path as sp
 
@@ -147,7 +145,7 @@ class Parser(object):
             sys.exit(1)
 
     def setup(self, text):
-        if isinstance(text, string_types):
+        if isinstance(text, str):
             # shlex does not handle Windows path
             # separators, so we must normalize to posix
             text = sp.convert_to_posix_path(text)
diff --git a/lib/spack/spack/provider_index.py b/lib/spack/spack/provider_index.py
index 254492fc21..1ffd19236b 100644
--- a/lib/spack/spack/provider_index.py
+++ b/lib/spack/spack/provider_index.py
@@ -5,8 +5,6 @@
 """Classes and functions to manage providers of virtual dependencies"""
 import itertools
 
-import six
-
 import spack.error
 import spack.util.spack_json as sjson
 
@@ -66,7 +64,7 @@ class _IndexBase(object):
         """
         result = set()
         # Allow string names to be passed as input, as well as specs
-        if isinstance(virtual_spec, six.string_types):
+        if isinstance(virtual_spec, str):
             virtual_spec = spack.spec.Spec(virtual_spec)
 
         # Add all the providers that satisfy the vpkg spec.
@@ -174,7 +172,7 @@ class ProviderIndex(_IndexBase):
         assert not self.repository.is_virtual_safe(spec.name), msg
 
         pkg_provided = self.repository.get_pkg_class(spec.name).provided
-        for provided_spec, provider_specs in six.iteritems(pkg_provided):
+        for provided_spec, provider_specs in pkg_provided.items():
             for provider_spec_readonly in provider_specs:
                 # TODO: fix this comment.
                 # We want satisfaction other than flags
@@ -310,7 +308,7 @@ def _transform(providers, transform_fun, out_mapping_type=dict):
 
     def mapiter(mappings):
         if isinstance(mappings, dict):
-            return six.iteritems(mappings)
+            return mappings.items()
         else:
             return iter(mappings)
 
diff --git a/lib/spack/spack/repo.py b/lib/spack/spack/repo.py
index e8c593f948..78b9f62b96 100644
--- a/lib/spack/spack/repo.py
+++ b/lib/spack/spack/repo.py
@@ -27,7 +27,6 @@ import uuid
 from typing import Dict  # novm
 
 import ruamel.yaml as yaml
-import six
 
 import llnl.util.filesystem as fs
 import llnl.util.lang
@@ -450,8 +449,7 @@ class FastPackageChecker(collections.abc.Mapping):
         return len(self._packages_to_stats)
 
 
-@six.add_metaclass(abc.ABCMeta)
-class Indexer(object):
+class Indexer(metaclass=abc.ABCMeta):
     """Adaptor for indexes that need to be generated when repos are updated."""
 
     def __init__(self, repository):
@@ -678,7 +676,7 @@ class RepoPath(object):
         # Add each repo to this path.
         for repo in repos:
             try:
-                if isinstance(repo, six.string_types):
+                if isinstance(repo, str):
                     repo = Repo(repo, cache=cache)
                 self.put_last(repo)
             except RepoError as e:
diff --git a/lib/spack/spack/reporters/cdash.py b/lib/spack/spack/reporters/cdash.py
index 2c57306412..413fc0626b 100644
--- a/lib/spack/spack/reporters/cdash.py
+++ b/lib/spack/spack/reporters/cdash.py
@@ -12,10 +12,8 @@ import re
 import socket
 import time
 import xml.sax.saxutils
-
-from six import iteritems, text_type
-from six.moves.urllib.parse import urlencode
-from six.moves.urllib.request import HTTPHandler, Request, build_opener
+from urllib.parse import urlencode
+from urllib.request import HTTPHandler, Request, build_opener
 
 import llnl.util.tty as tty
 from llnl.util.filesystem import working_dir
@@ -158,7 +156,7 @@ class CDash(Reporter):
                 if cdash_phase not in phases_encountered:
                     phases_encountered.append(cdash_phase)
                 report_data[cdash_phase]["loglines"].append(
-                    text_type("{0} output for {1}:".format(cdash_phase, package["name"]))
+                    str("{0} output for {1}:".format(cdash_phase, package["name"]))
                 )
             elif cdash_phase:
                 report_data[cdash_phase]["loglines"].append(xml.sax.saxutils.escape(line))
@@ -289,7 +287,7 @@ class CDash(Reporter):
         # Generate a report for this package.
         # The first line just says "Testing package name-hash"
         report_data["test"]["loglines"].append(
-            text_type("{0} output for {1}:".format("test", package["name"]))
+            str("{0} output for {1}:".format("test", package["name"]))
         )
         for line in package["stdout"].splitlines()[1:]:
             report_data["test"]["loglines"].append(xml.sax.saxutils.escape(line))
@@ -502,7 +500,7 @@ class CDash(Reporter):
     def finalize_report(self):
         if self.buildIds:
             tty.msg("View your build results here:")
-            for package_name, buildid in iteritems(self.buildIds):
+            for package_name, buildid in self.buildIds.items():
                 # Construct and display a helpful link if CDash responded with
                 # a buildId.
                 build_url = self.cdash_upload_url
diff --git a/lib/spack/spack/s3_handler.py b/lib/spack/spack/s3_handler.py
index c867642603..74eb8466ce 100644
--- a/lib/spack/spack/s3_handler.py
+++ b/lib/spack/spack/s3_handler.py
@@ -3,13 +3,11 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import urllib.error
+import urllib.request
+import urllib.response
 from io import BufferedReader, IOBase
 
-import six
-import six.moves.urllib.error as urllib_error
-import six.moves.urllib.request as urllib_request
-import six.moves.urllib.response as urllib_response
-
 import spack.util.s3 as s3_util
 import spack.util.url as url_util
 
@@ -63,32 +61,32 @@ def _s3_open(url):
     return url, headers, stream
 
 
-class UrllibS3Handler(urllib_request.HTTPSHandler):
+class UrllibS3Handler(urllib.request.HTTPSHandler):
     def s3_open(self, req):
         orig_url = req.get_full_url()
         from botocore.exceptions import ClientError  # type: ignore[import]
 
         try:
             url, headers, stream = _s3_open(orig_url)
-            return urllib_response.addinfourl(stream, headers, url)
+            return urllib.response.addinfourl(stream, headers, url)
         except ClientError as err:
             # if no such [KEY], but [KEY]/index.html exists,
             # return that, instead.
             if err.response["Error"]["Code"] == "NoSuchKey":
                 try:
                     _, headers, stream = _s3_open(url_util.join(orig_url, "index.html"))
-                    return urllib_response.addinfourl(stream, headers, orig_url)
+                    return urllib.response.addinfourl(stream, headers, orig_url)
 
                 except ClientError as err2:
                     if err.response["Error"]["Code"] == "NoSuchKey":
                         # raise original error
-                        raise six.raise_from(urllib_error.URLError(err), err)
+                        raise urllib.error.URLError(err) from err
 
-                    raise six.raise_from(urllib_error.URLError(err2), err2)
+                    raise urllib.error.URLError(err2) from err2
 
-            raise six.raise_from(urllib_error.URLError(err), err)
+            raise urllib.error.URLError(err) from err
 
 
-S3OpenerDirector = urllib_request.build_opener(UrllibS3Handler())
+S3OpenerDirector = urllib.request.build_opener(UrllibS3Handler())
 
 open = S3OpenerDirector.open
diff --git a/lib/spack/spack/schema/__init__.py b/lib/spack/spack/schema/__init__.py
index 54f645fd5c..33d930e2c6 100644
--- a/lib/spack/spack/schema/__init__.py
+++ b/lib/spack/spack/schema/__init__.py
@@ -3,11 +3,8 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 """This module contains jsonschema files for all of Spack's YAML formats."""
-
 import warnings
 
-import six
-
 import llnl.util.lang
 import llnl.util.tty
 
@@ -45,7 +42,7 @@ def _make_validator():
 
         # Retrieve the template message
         msg_str_or_func = deprecated["message"]
-        if isinstance(msg_str_or_func, six.string_types):
+        if isinstance(msg_str_or_func, str):
             msg = msg_str_or_func.format(properties=deprecated_properties)
         else:
             msg = msg_str_or_func(instance, deprecated_properties)
diff --git a/lib/spack/spack/schema/config.py b/lib/spack/spack/schema/config.py
index 96e34a051a..240f99e8b0 100644
--- a/lib/spack/spack/schema/config.py
+++ b/lib/spack/spack/schema/config.py
@@ -2,13 +2,11 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
 """Schema for config.yaml configuration file.
 
 .. literalinclude:: _spack_root/lib/spack/spack/schema/config.py
    :lines: 13-
 """
-import six
 
 from llnl.util.lang import union_dicts
 
@@ -124,7 +122,7 @@ def update(data):
     changed = False
 
     install_tree = data.get("install_tree", None)
-    if isinstance(install_tree, six.string_types):
+    if isinstance(install_tree, str):
         # deprecated short-form install tree
         # add value as `root` in updated install_tree
         data["install_tree"] = {"root": install_tree}
@@ -148,7 +146,7 @@ def update(data):
         changed = True
 
     shared_linking = data.get("shared_linking", None)
-    if isinstance(shared_linking, six.string_types):
+    if isinstance(shared_linking, str):
         # deprecated short-form shared_linking: rpath/runpath
         # add value as `type` in updated shared_linking
         data["shared_linking"] = {"type": shared_linking, "bind": False}
diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index 844252c97b..c070741c2c 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -14,8 +14,6 @@ import re
 import types
 import warnings
 
-from six import string_types
-
 import archspec.cpu
 
 try:
@@ -213,7 +211,7 @@ def build_criteria_names(costs, tuples):
 
 
 def issequence(obj):
-    if isinstance(obj, string_types):
+    if isinstance(obj, str):
         return False
     return isinstance(obj, (collections.abc.Sequence, types.GeneratorType))
 
@@ -225,7 +223,7 @@ def listify(args):
 
 
 def packagize(pkg):
-    if isinstance(pkg, string_types):
+    if isinstance(pkg, str):
         return spack.repo.path.get_pkg_class(pkg)
     else:
         return pkg
@@ -949,7 +947,7 @@ class SpackSolverSetup(object):
         """Manipulate requirements from packages.yaml, and return a list of tuples
         with a uniform structure (name, policy, requirements).
         """
-        if isinstance(requirements, string_types):
+        if isinstance(requirements, str):
             rules = [(pkg_name, "one_of", [requirements])]
         else:
             rules = []
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 015c5b8061..401be97858 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -81,6 +81,7 @@ expansion when it is the first character in an id typed on the command line.
 """
 import collections
 import collections.abc
+import io
 import itertools
 import os
 import re
@@ -88,7 +89,6 @@ import sys
 import warnings
 
 import ruamel.yaml as yaml
-import six
 
 import llnl.util.filesystem as fs
 import llnl.util.lang as lang
@@ -274,11 +274,11 @@ class ArchSpec(object):
             other = spec_or_platform_tuple
             platform_tuple = other.platform, other.os, other.target
 
-        elif isinstance(spec_or_platform_tuple, (six.string_types, tuple)):
+        elif isinstance(spec_or_platform_tuple, (str, tuple)):
             spec_fields = spec_or_platform_tuple
 
             # Normalize the string to a tuple
-            if isinstance(spec_or_platform_tuple, six.string_types):
+            if isinstance(spec_or_platform_tuple, str):
                 spec_fields = spec_or_platform_tuple.split("-")
                 if len(spec_fields) != 3:
                     msg = "cannot construct an ArchSpec from {0!s}"
@@ -534,7 +534,6 @@ class ArchSpec(object):
     @property
     def concrete(self):
         """True if the spec is concrete, False otherwise"""
-        # return all(v for k, v in six.iteritems(self.to_cmp_dict()))
         return self.platform and self.os and self.target and self.target_concrete
 
     @property
@@ -584,7 +583,7 @@ class CompilerSpec(object):
             arg = args[0]
             # If there is one argument, it's either another CompilerSpec
             # to copy or a string to parse
-            if isinstance(arg, six.string_types):
+            if isinstance(arg, str):
                 c = SpecParser().parse_compiler(arg)
                 self.name = c.name
                 self.versions = c.versions
@@ -1335,7 +1334,7 @@ class Spec(object):
         # Build spec should be the actual build spec unless marked dirty.
         self._build_spec = None
 
-        if isinstance(spec_like, six.string_types):
+        if isinstance(spec_like, str):
             spec_list = SpecParser(self).parse(spec_like)
             if len(spec_list) > 1:
                 raise ValueError("More than one spec in string: " + spec_like)
@@ -1538,7 +1537,7 @@ class Spec(object):
             new_vals = tuple(kwargs.get(arg, None) for arg in arch_attrs)
             self.architecture = ArchSpec(new_vals)
         else:
-            new_attrvals = [(a, v) for a, v in six.iteritems(kwargs) if a in arch_attrs]
+            new_attrvals = [(a, v) for a, v in kwargs.items() if a in arch_attrs]
             for new_attr, new_value in new_attrvals:
                 if getattr(self.architecture, new_attr):
                     raise DuplicateArchitectureError(
@@ -1932,9 +1931,7 @@ class Spec(object):
             package_hash = self._package_hash
 
             # Full hashes are in bytes
-            if not isinstance(package_hash, six.text_type) and isinstance(
-                package_hash, six.binary_type
-            ):
+            if not isinstance(package_hash, str) and isinstance(package_hash, bytes):
                 package_hash = package_hash.decode("utf-8")
             d["package_hash"] = package_hash
 
@@ -2204,7 +2201,7 @@ class Spec(object):
             else:
                 elt = dep
                 dep_name = dep["name"]
-            if isinstance(elt, six.string_types):
+            if isinstance(elt, str):
                 # original format, elt is just the dependency hash.
                 dep_hash, deptypes = elt, ["build", "link"]
             elif isinstance(elt, tuple):
@@ -2390,7 +2387,7 @@ class Spec(object):
             # Recurse on dependencies
             for s, s_dependencies in dep_like.items():
 
-                if isinstance(s, six.string_types):
+                if isinstance(s, str):
                     dag_node, dependency_types = name_and_dependency_types(s)
                 else:
                     dag_node, dependency_types = spec_and_dependency_types(s)
@@ -2469,10 +2466,7 @@ class Spec(object):
             data = yaml.load(stream)
             return Spec.from_dict(data)
         except yaml.error.MarkedYAMLError as e:
-            raise six.raise_from(
-                syaml.SpackYAMLError("error parsing YAML spec:", str(e)),
-                e,
-            )
+            raise syaml.SpackYAMLError("error parsing YAML spec:", str(e)) from e
 
     @staticmethod
     def from_json(stream):
@@ -2485,10 +2479,7 @@ class Spec(object):
             data = sjson.load(stream)
             return Spec.from_dict(data)
         except Exception as e:
-            raise six.raise_from(
-                sjson.SpackJSONError("error parsing JSON spec:", str(e)),
-                e,
-            )
+            raise sjson.SpackJSONError("error parsing JSON spec:", str(e)) from e
 
     @staticmethod
     def extract_json_from_clearsig(data):
@@ -3112,10 +3103,7 @@ class Spec(object):
             # with inconsistent constraints.  Users cannot produce
             # inconsistent specs like this on the command line: the
             # parser doesn't allow it. Spack must be broken!
-            raise six.raise_from(
-                InconsistentSpecError("Invalid Spec DAG: %s" % e.message),
-                e,
-            )
+            raise InconsistentSpecError("Invalid Spec DAG: %s" % e.message) from e
 
     def index(self, deptype="all"):
         """Return a dictionary that points to all the dependencies in this
@@ -4214,7 +4202,7 @@ class Spec(object):
         color = kwargs.get("color", False)
         transform = kwargs.get("transform", {})
 
-        out = six.StringIO()
+        out = io.StringIO()
 
         def write(s, c=None):
             f = clr.cescape(s)
@@ -4437,7 +4425,7 @@ class Spec(object):
         token_transforms = dict((k.upper(), v) for k, v in kwargs.get("transform", {}).items())
 
         length = len(format_string)
-        out = six.StringIO()
+        out = io.StringIO()
         named = escape = compiler = False
         named_str = fmt = ""
 
@@ -5153,7 +5141,7 @@ class SpecParser(spack.parse.Parser):
                         self.unexpected_token()
 
         except spack.parse.ParseError as e:
-            raise six.raise_from(SpecParseError(e), e)
+            raise SpecParseError(e) from e
 
         # Generate lookups for git-commit-based versions
         for spec in specs:
diff --git a/lib/spack/spack/spec_list.py b/lib/spack/spack/spec_list.py
index ffbf2bfaf9..cdc7796dcc 100644
--- a/lib/spack/spack/spec_list.py
+++ b/lib/spack/spack/spec_list.py
@@ -4,8 +4,6 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import itertools
 
-from six import string_types
-
 import spack.variant
 from spack.error import SpackError
 from spack.spec import Spec
@@ -21,7 +19,7 @@ class SpecList(object):
         self._reference = reference  # TODO: Do we need defensive copy here?
 
         # Validate yaml_list before assigning
-        if not all(isinstance(s, string_types) or isinstance(s, (list, dict)) for s in yaml_list):
+        if not all(isinstance(s, str) or isinstance(s, (list, dict)) for s in yaml_list):
             raise ValueError(
                 "yaml_list can contain only valid YAML types!  Found:\n  %s"
                 % [type(s) for s in yaml_list]
@@ -91,7 +89,7 @@ class SpecList(object):
         remove = [
             s
             for s in self.yaml_list
-            if (isinstance(s, string_types) and not s.startswith("$")) and Spec(s) == Spec(spec)
+            if (isinstance(s, str) and not s.startswith("$")) and Spec(s) == Spec(spec)
         ]
         if not remove:
             msg = "Cannot remove %s from SpecList %s\n" % (spec, self.name)
@@ -145,7 +143,7 @@ class SpecList(object):
 
             for item in yaml:
                 # if it's a reference, expand it
-                if isinstance(item, string_types) and item.startswith("$"):
+                if isinstance(item, str) and item.startswith("$"):
                     # replace the reference and apply the sigil if needed
                     name, sigil = self._parse_reference(item)
                     referent = [
diff --git a/lib/spack/spack/stage.py b/lib/spack/spack/stage.py
index 62e05d504e..ee9f8a122b 100644
--- a/lib/spack/spack/stage.py
+++ b/lib/spack/spack/stage.py
@@ -16,8 +16,6 @@ import sys
 import tempfile
 from typing import Dict  # novm
 
-from six import iteritems, string_types
-
 import llnl.util.lang
 import llnl.util.tty as tty
 from llnl.util.filesystem import (
@@ -171,7 +169,7 @@ def get_stage_root():
 
     if _stage_root is None:
         candidates = spack.config.get("config:build_stage")
-        if isinstance(candidates, string_types):
+        if isinstance(candidates, str):
             candidates = [candidates]
 
         resolved_candidates = _resolve_paths(candidates)
@@ -288,7 +286,7 @@ class Stage(object):
         """
         # TODO: fetch/stage coupling needs to be reworked -- the logic
         # TODO: here is convoluted and not modular enough.
-        if isinstance(url_or_fetch_strategy, string_types):
+        if isinstance(url_or_fetch_strategy, str):
             self.fetcher = fs.from_url_scheme(url_or_fetch_strategy)
         elif isinstance(url_or_fetch_strategy, fs.FetchStrategy):
             self.fetcher = url_or_fetch_strategy
@@ -709,7 +707,7 @@ class ResourceStage(Stage):
             else:
                 raise
 
-        for key, value in iteritems(placement):
+        for key, value in placement.items():
             destination_path = os.path.join(target_path, value)
             source_path = os.path.join(self.source_path, key)
 
@@ -903,7 +901,7 @@ def get_checksums_for_versions(url_dict, name, **kwargs):
         "",
         *llnl.util.lang.elide_list(
             ["{0:{1}}  {2}".format(str(v), max_len, url_dict[v]) for v in sorted_versions]
-        )
+        ),
     )
     print()
 
diff --git a/lib/spack/spack/store.py b/lib/spack/spack/store.py
index 4e38d0c634..d9440f2aed 100644
--- a/lib/spack/spack/store.py
+++ b/lib/spack/spack/store.py
@@ -21,8 +21,6 @@ import contextlib
 import os
 import re
 
-import six
-
 import llnl.util.lang
 import llnl.util.tty as tty
 
@@ -69,7 +67,7 @@ def parse_install_tree(config_dict):
     install_tree = config_dict.get("install_tree", {})
 
     padded_length = False
-    if isinstance(install_tree, six.string_types):
+    if isinstance(install_tree, str):
         tty.warn("Using deprecated format for configuring install_tree")
         unpadded_root = install_tree
         unpadded_root = spack.util.path.canonicalize_path(unpadded_root)
@@ -309,7 +307,7 @@ def find(constraints, multiple=False, query_fn=None, **kwargs):
         List of matching specs
     """
     # Normalize input to list of specs
-    if isinstance(constraints, six.string_types):
+    if isinstance(constraints, str):
         constraints = [spack.spec.Spec(constraints)]
 
     matching_specs, errors = [], []
diff --git a/lib/spack/spack/target.py b/lib/spack/spack/target.py
index d51ca3aa99..fd8830fffd 100644
--- a/lib/spack/spack/target.py
+++ b/lib/spack/spack/target.py
@@ -5,8 +5,6 @@
 import functools
 import warnings
 
-import six
-
 import archspec.cpu
 
 import llnl.util.tty as tty
@@ -24,7 +22,7 @@ def _ensure_other_is_target(method):
 
     @functools.wraps(method)
     def _impl(self, other):
-        if isinstance(other, six.string_types):
+        if isinstance(other, str):
             other = Target(other)
 
         if not isinstance(other, Target):
@@ -95,7 +93,7 @@ class Target(object):
     def from_dict_or_value(dict_or_value):
         # A string here represents a generic target (like x86_64 or ppc64) or
         # a custom micro-architecture
-        if isinstance(dict_or_value, six.string_types):
+        if isinstance(dict_or_value, str):
             return Target(dict_or_value)
 
         # TODO: From a dict we actually retrieve much more information than
diff --git a/lib/spack/spack/tengine.py b/lib/spack/spack/tengine.py
index 75dae5c9c1..0965dc0179 100644
--- a/lib/spack/spack/tengine.py
+++ b/lib/spack/spack/tengine.py
@@ -6,8 +6,6 @@ import itertools
 import textwrap
 from typing import List  # novm
 
-import six
-
 import llnl.util.lang
 
 import spack.config
@@ -57,7 +55,7 @@ class ContextMeta(type):
 context_property = ContextMeta.context_property
 
 
-class Context(six.with_metaclass(ContextMeta, object)):
+class Context(metaclass=ContextMeta):
     """Base class for context classes that are used with the template
     engine.
     """
diff --git a/lib/spack/spack/test/cmd/build_env.py b/lib/spack/spack/test/cmd/build_env.py
index 16d363eff4..2ba9a008dc 100644
--- a/lib/spack/spack/test/cmd/build_env.py
+++ b/lib/spack/spack/test/cmd/build_env.py
@@ -2,9 +2,9 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import pickle
 
 import pytest
-from six.moves import cPickle
 
 from spack.main import SpackCommand
 
@@ -52,6 +52,6 @@ def test_dump(tmpdir):
 def test_pickle(tmpdir):
     with tmpdir.as_cwd():
         build_env("--pickle", _out_file, "zlib")
-        environment = cPickle.load(open(_out_file, "rb"))
+        environment = pickle.load(open(_out_file, "rb"))
         assert type(environment) == dict
         assert "PATH" in environment
diff --git a/lib/spack/spack/test/cmd/env.py b/lib/spack/spack/test/cmd/env.py
index 9611ae5748..64aaf3c225 100644
--- a/lib/spack/spack/test/cmd/env.py
+++ b/lib/spack/spack/test/cmd/env.py
@@ -4,13 +4,13 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import filecmp
 import glob
+import io
 import os
 import shutil
 import sys
 from argparse import Namespace
 
 import pytest
-from six import StringIO
 
 import llnl.util.filesystem as fs
 import llnl.util.link_tree
@@ -507,7 +507,7 @@ def test_env_repo():
 
 def test_user_removed_spec():
     """Ensure a user can remove from any position in the spack.yaml file."""
-    initial_yaml = StringIO(
+    initial_yaml = io.StringIO(
         """\
 env:
   specs:
@@ -545,7 +545,7 @@ env:
 
 def test_init_from_lockfile(tmpdir):
     """Test that an environment can be instantiated from a lockfile."""
-    initial_yaml = StringIO(
+    initial_yaml = io.StringIO(
         """\
 env:
   specs:
@@ -573,7 +573,7 @@ env:
 
 def test_init_from_yaml(tmpdir):
     """Test that an environment can be instantiated from a lockfile."""
-    initial_yaml = StringIO(
+    initial_yaml = io.StringIO(
         """\
 env:
   specs:
@@ -602,7 +602,7 @@ def test_env_view_external_prefix(tmpdir_factory, mutable_database, mock_package
     fake_bin = fake_prefix.join("bin")
     fake_bin.ensure(dir=True)
 
-    initial_yaml = StringIO(
+    initial_yaml = io.StringIO(
         """\
 env:
   specs:
@@ -611,7 +611,7 @@ env:
 """
     )
 
-    external_config = StringIO(
+    external_config = io.StringIO(
         """\
 packages:
   a:
@@ -682,7 +682,7 @@ env:
     mpileaks:
       version: [2.2]
 """
-    _env_create("test", StringIO(test_config))
+    _env_create("test", io.StringIO(test_config))
 
     e = ev.read("test")
     with e:
@@ -699,7 +699,7 @@ spack:
   - /no/such/directory
   - no/such/file.yaml
 """
-    _env_create(env_name, StringIO(test_config))
+    _env_create(env_name, io.StringIO(test_config))
 
     e = ev.read(env_name)
     with pytest.raises(spack.config.ConfigFileError) as exc:
@@ -723,7 +723,7 @@ def test_env_with_include_config_files_same_basename():
                 [libelf, mpileaks]
             """
 
-    _env_create("test", StringIO(test_config))
+    _env_create("test", io.StringIO(test_config))
     e = ev.read("test")
 
     fs.mkdirp(os.path.join(e.path, "path", "to"))
@@ -788,7 +788,7 @@ def test_env_with_included_config_file(packages_file):
     include_filename = "included-config.yaml"
     test_config = mpileaks_env_config(os.path.join(".", include_filename))
 
-    _env_create("test", StringIO(test_config))
+    _env_create("test", io.StringIO(test_config))
     e = ev.read("test")
 
     included_path = os.path.join(e.path, include_filename)
@@ -842,7 +842,7 @@ def test_env_with_included_config_scope(tmpdir, packages_file):
     test_config = mpileaks_env_config(config_scope_path)
 
     # Create the environment
-    _env_create("test", StringIO(test_config))
+    _env_create("test", io.StringIO(test_config))
 
     e = ev.read("test")
 
@@ -868,7 +868,7 @@ def test_env_with_included_config_var_path(packages_file):
     config_var_path = os.path.join("$tempdir", "included-config.yaml")
     test_config = mpileaks_env_config(config_var_path)
 
-    _env_create("test", StringIO(test_config))
+    _env_create("test", io.StringIO(test_config))
     e = ev.read("test")
 
     config_real_path = substitute_path_variables(config_var_path)
@@ -893,7 +893,7 @@ env:
   specs:
   - mpileaks
 """
-    _env_create("test", StringIO(test_config))
+    _env_create("test", io.StringIO(test_config))
     e = ev.read("test")
 
     with open(os.path.join(e.path, "included-config.yaml"), "w") as f:
@@ -926,7 +926,7 @@ env:
   specs:
   - mpileaks
 """
-    _env_create("test", StringIO(test_config))
+    _env_create("test", io.StringIO(test_config))
     e = ev.read("test")
 
     with open(os.path.join(e.path, "high-config.yaml"), "w") as f:
@@ -1263,7 +1263,7 @@ env:
   specs:
   - mpileaks
 """
-    _env_create("test", StringIO(test_config))
+    _env_create("test", io.StringIO(test_config))
 
     with ev.read("test"):
         install("--fake")
@@ -2672,7 +2672,7 @@ spack:
       roots:
         tcl: modules
 """
-    _env_create("test", StringIO(spack_yaml))
+    _env_create("test", io.StringIO(spack_yaml))
 
     with ev.read("test") as e:
         install()
@@ -2707,7 +2707,7 @@ spack:
       roots:
         tcl: full_modules
 """
-    _env_create("test", StringIO(spack_yaml))
+    _env_create("test", io.StringIO(spack_yaml))
 
     with ev.read("test") as e:
         install()
@@ -3116,7 +3116,7 @@ def test_environment_depfile_makefile(depfile_flags, expected_installs, tmpdir,
             makefile,
             "--make-disable-jobserver",
             "--make-target-prefix=prefix",
-            *depfile_flags
+            *depfile_flags,
         )
 
     # Do make dry run.
diff --git a/lib/spack/spack/test/cmd/install.py b/lib/spack/spack/test/cmd/install.py
index 67e0dd3f80..d1993be777 100644
--- a/lib/spack/spack/test/cmd/install.py
+++ b/lib/spack/spack/test/cmd/install.py
@@ -2,8 +2,8 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
 import argparse
+import builtins
 import filecmp
 import itertools
 import os
@@ -12,7 +12,6 @@ import sys
 import time
 
 import pytest
-from six.moves import builtins
 
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
diff --git a/lib/spack/spack/test/compilers/basics.py b/lib/spack/spack/test/compilers/basics.py
index 4e03c9a288..598e44f4fc 100644
--- a/lib/spack/spack/test/compilers/basics.py
+++ b/lib/spack/spack/test/compilers/basics.py
@@ -9,7 +9,6 @@ import sys
 from copy import copy
 
 import pytest
-from six import iteritems
 
 import llnl.util.filesystem as fs
 
@@ -73,7 +72,7 @@ def test_get_compiler_duplicates(config):
     )
 
     assert len(cfg_file_to_duplicates) == 1
-    cfg_file, duplicates = next(iteritems(cfg_file_to_duplicates))
+    cfg_file, duplicates = next(iter(cfg_file_to_duplicates.items()))
     assert len(duplicates) == 1
 
 
diff --git a/lib/spack/spack/test/config.py b/lib/spack/spack/test/config.py
index f8b1e44547..e310519afd 100644
--- a/lib/spack/spack/test/config.py
+++ b/lib/spack/spack/test/config.py
@@ -5,13 +5,13 @@
 
 import collections
 import getpass
+import io
 import os
 import sys
 import tempfile
 from datetime import date
 
 import pytest
-from six import StringIO
 
 import llnl.util.tty as tty
 from llnl.util.filesystem import getuid, join_path, mkdirp, touch, touchp
@@ -1012,7 +1012,7 @@ def test_write_empty_single_file_scope(tmpdir):
 
 def check_schema(name, file_contents):
     """Check a Spack YAML schema against some data"""
-    f = StringIO(file_contents)
+    f = io.StringIO(file_contents)
     data = syaml.load_config(f)
     spack.config.validate(data, name)
 
diff --git a/lib/spack/spack/test/env.py b/lib/spack/spack/test/env.py
index 60056e397a..2de80c43e3 100644
--- a/lib/spack/spack/test/env.py
+++ b/lib/spack/spack/test/env.py
@@ -2,12 +2,11 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
 """Test environment internals without CLI"""
+import io
 import sys
 
 import pytest
-from six import StringIO
 
 import spack.environment as ev
 import spack.spec
@@ -79,7 +78,7 @@ env:
 
 
 def test_env_change_spec_in_definition(tmpdir, mock_packages, config, mutable_mock_env_path):
-    initial_yaml = StringIO(_test_matrix_yaml)
+    initial_yaml = io.StringIO(_test_matrix_yaml)
     e = ev.create("test", initial_yaml)
     e.concretize()
     e.write()
@@ -96,7 +95,7 @@ def test_env_change_spec_in_definition(tmpdir, mock_packages, config, mutable_mo
 def test_env_change_spec_in_matrix_raises_error(
     tmpdir, mock_packages, config, mutable_mock_env_path
 ):
-    initial_yaml = StringIO(_test_matrix_yaml)
+    initial_yaml = io.StringIO(_test_matrix_yaml)
     e = ev.create("test", initial_yaml)
     e.concretize()
     e.write()
diff --git a/lib/spack/spack/test/graph.py b/lib/spack/spack/test/graph.py
index dc7181538e..b906548d7f 100644
--- a/lib/spack/spack/test/graph.py
+++ b/lib/spack/spack/test/graph.py
@@ -2,10 +2,10 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import io
 import sys
 
 import pytest
-import six
 
 import spack.graph
 import spack.repo
@@ -25,7 +25,7 @@ def test_static_graph_mpileaks(config, mock_packages):
     """Test a static spack graph for a simple package."""
     s = spack.spec.Spec("mpileaks").normalized()
 
-    stream = six.StringIO()
+    stream = io.StringIO()
     spack.graph.graph_dot([s], static=True, out=stream)
 
     dot = stream.getvalue()
@@ -52,7 +52,7 @@ def test_static_graph_mpileaks(config, mock_packages):
 def test_dynamic_dot_graph_mpileaks(mock_packages, config):
     """Test dynamically graphing the mpileaks package."""
     s = spack.spec.Spec("mpileaks").concretized()
-    stream = six.StringIO()
+    stream = io.StringIO()
     spack.graph.graph_dot([s], static=False, out=stream)
     dot = stream.getvalue()
 
@@ -83,7 +83,7 @@ def test_ascii_graph_mpileaks(config, mock_packages, monkeypatch):
     monkeypatch.setattr(spack.graph.AsciiGraph, "_node_label", lambda self, node: node.name)
     s = spack.spec.Spec("mpileaks").concretized()
 
-    stream = six.StringIO()
+    stream = io.StringIO()
     graph = spack.graph.AsciiGraph()
     graph.write(s, out=stream, color=False)
     graph_str = stream.getvalue()
diff --git a/lib/spack/spack/test/llnl/util/file_list.py b/lib/spack/spack/test/llnl/util/file_list.py
index a6a7ef3fa9..682dbc6e86 100644
--- a/lib/spack/spack/test/llnl/util/file_list.py
+++ b/lib/spack/spack/test/llnl/util/file_list.py
@@ -8,7 +8,6 @@ import os.path
 import sys
 
 import pytest
-import six
 
 from llnl.util.filesystem import (
     HeaderList,
@@ -320,7 +319,7 @@ def test_searching_order(search_fn, search_list, root, kwargs):
     rlist = list(reversed(result))
 
     # At this point make sure the search list is a sequence
-    if isinstance(search_list, six.string_types):
+    if isinstance(search_list, str):
         search_list = [search_list]
 
     # Discard entries in the order they appear in search list
diff --git a/lib/spack/spack/test/provider_index.py b/lib/spack/spack/test/provider_index.py
index c698a7b87e..f840056798 100644
--- a/lib/spack/spack/test/provider_index.py
+++ b/lib/spack/spack/test/provider_index.py
@@ -18,7 +18,7 @@ Tests assume that mock packages provide this::
                     mpi@:10.0: set([zmpi])},
     'stuff': {stuff: set([externalvirtual])}}
 """
-from six import StringIO
+import io
 
 import spack.repo
 from spack.provider_index import ProviderIndex
@@ -28,10 +28,10 @@ from spack.spec import Spec
 def test_provider_index_round_trip(mock_packages):
     p = ProviderIndex(specs=spack.repo.all_package_names(), repository=spack.repo.path)
 
-    ostream = StringIO()
+    ostream = io.StringIO()
     p.to_json(ostream)
 
-    istream = StringIO(ostream.getvalue())
+    istream = io.StringIO(ostream.getvalue())
     q = ProviderIndex.from_json(istream, repository=spack.repo.path)
 
     assert p == q
diff --git a/lib/spack/spack/test/tag.py b/lib/spack/spack/test/tag.py
index 68414c1288..91d1418207 100644
--- a/lib/spack/spack/test/tag.py
+++ b/lib/spack/spack/test/tag.py
@@ -3,9 +3,9 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 """Tests for tag index cache files."""
+import io
 
 import pytest
-from six import StringIO
 
 import spack.cmd.install
 import spack.tag
@@ -40,7 +40,7 @@ more_tags_json = """
 
 
 def test_tag_copy(mock_packages):
-    index = spack.tag.TagIndex.from_json(StringIO(tags_json), repository=mock_packages)
+    index = spack.tag.TagIndex.from_json(io.StringIO(tags_json), repository=mock_packages)
     new_index = index.copy()
 
     assert index.tags == new_index.tags
@@ -100,25 +100,27 @@ def test_tag_index_round_trip(mock_packages):
     mock_index = spack.repo.path.tag_index
     assert mock_index.tags
 
-    ostream = StringIO()
+    ostream = io.StringIO()
     mock_index.to_json(ostream)
 
-    istream = StringIO(ostream.getvalue())
+    istream = io.StringIO(ostream.getvalue())
     new_index = spack.tag.TagIndex.from_json(istream, repository=mock_packages)
 
     assert mock_index == new_index
 
 
 def test_tag_equal(mock_packages):
-    first_index = spack.tag.TagIndex.from_json(StringIO(tags_json), repository=mock_packages)
-    second_index = spack.tag.TagIndex.from_json(StringIO(tags_json), repository=mock_packages)
+    first_index = spack.tag.TagIndex.from_json(io.StringIO(tags_json), repository=mock_packages)
+    second_index = spack.tag.TagIndex.from_json(io.StringIO(tags_json), repository=mock_packages)
 
     assert first_index == second_index
 
 
 def test_tag_merge(mock_packages):
-    first_index = spack.tag.TagIndex.from_json(StringIO(tags_json), repository=mock_packages)
-    second_index = spack.tag.TagIndex.from_json(StringIO(more_tags_json), repository=mock_packages)
+    first_index = spack.tag.TagIndex.from_json(io.StringIO(tags_json), repository=mock_packages)
+    second_index = spack.tag.TagIndex.from_json(
+        io.StringIO(more_tags_json), repository=mock_packages
+    )
 
     assert first_index != second_index
 
@@ -139,14 +141,14 @@ def test_tag_merge(mock_packages):
 def test_tag_not_dict(mock_packages):
     list_json = "[]"
     with pytest.raises(spack.tag.TagIndexError) as e:
-        spack.tag.TagIndex.from_json(StringIO(list_json), repository=mock_packages)
+        spack.tag.TagIndex.from_json(io.StringIO(list_json), repository=mock_packages)
         assert "not a dict" in str(e)
 
 
 def test_tag_no_tags(mock_packages):
     pkg_json = '{"packages": []}'
     with pytest.raises(spack.tag.TagIndexError) as e:
-        spack.tag.TagIndex.from_json(StringIO(pkg_json), repository=mock_packages)
+        spack.tag.TagIndex.from_json(io.StringIO(pkg_json), repository=mock_packages)
         assert "does not start with" in str(e)
 
 
diff --git a/lib/spack/spack/test/util/unparse/unparse.py b/lib/spack/spack/test/util/unparse/unparse.py
index 82148c9dc8..986ba7e262 100644
--- a/lib/spack/spack/test/util/unparse/unparse.py
+++ b/lib/spack/spack/test/util/unparse/unparse.py
@@ -6,14 +6,9 @@ import ast
 import codecs
 import os
 import sys
+import tokenize
 
 import pytest
-import six
-
-if six.PY3:
-    import tokenize
-else:
-    from lib2to3.pgen2 import tokenize
 
 import spack.util.unparse
 
@@ -25,14 +20,10 @@ pytestmark = pytest.mark.skipif(
 def read_pyfile(filename):
     """Read and return the contents of a Python source file (as a
     string), taking into account the file encoding."""
-    if six.PY3:
-        with open(filename, "rb") as pyfile:
-            encoding = tokenize.detect_encoding(pyfile.readline)[0]
-        with codecs.open(filename, "r", encoding=encoding) as pyfile:
-            source = pyfile.read()
-    else:
-        with open(filename, "r") as pyfile:
-            source = pyfile.read()
+    with open(filename, "rb") as pyfile:
+        encoding = tokenize.detect_encoding(pyfile.readline)[0]
+    with codecs.open(filename, "r", encoding=encoding) as pyfile:
+        source = pyfile.read()
     return source
 
 
@@ -341,16 +332,9 @@ def test_huge_float():
     check_ast_roundtrip("-1e1000j")
 
 
-@pytest.mark.skipif(not six.PY2, reason="Only works for Python 2")
-def test_min_int27():
-    check_ast_roundtrip(str(-sys.maxint - 1))
-    check_ast_roundtrip("-(%s)" % (sys.maxint + 1))
-
-
-@pytest.mark.skipif(not six.PY3, reason="Only works for Python 3")
 def test_min_int30():
-    check_ast_roundtrip(str(-(2 ** 31)))
-    check_ast_roundtrip(str(-(2 ** 63)))
+    check_ast_roundtrip(str(-(2**31)))
+    check_ast_roundtrip(str(-(2**63)))
 
 
 def test_imaginary_literals():
@@ -358,9 +342,6 @@ def test_imaginary_literals():
     check_ast_roundtrip("-7j")
     check_ast_roundtrip("0j")
     check_ast_roundtrip("-0j")
-    if six.PY2:
-        check_ast_roundtrip("-(7j)")
-        check_ast_roundtrip("-(0j)")
 
 
 def test_negative_zero():
@@ -391,12 +372,11 @@ def test_function_arguments():
     check_ast_roundtrip("def f(a, b = 2): pass")
     check_ast_roundtrip("def f(a = 5, b = 2): pass")
     check_ast_roundtrip("def f(*args, **kwargs): pass")
-    if six.PY3:
-        check_ast_roundtrip("def f(*, a = 1, b = 2): pass")
-        check_ast_roundtrip("def f(*, a = 1, b): pass")
-        check_ast_roundtrip("def f(*, a, b = 2): pass")
-        check_ast_roundtrip("def f(a, b = None, *, c, **kwds): pass")
-        check_ast_roundtrip("def f(a=2, *args, c=5, d, **kwds): pass")
+    check_ast_roundtrip("def f(*, a = 1, b = 2): pass")
+    check_ast_roundtrip("def f(*, a = 1, b): pass")
+    check_ast_roundtrip("def f(*, a, b = 2): pass")
+    check_ast_roundtrip("def f(a, b = None, *, c, **kwds): pass")
+    check_ast_roundtrip("def f(a=2, *args, c=5, d, **kwds): pass")
 
 
 def test_relative_import():
@@ -407,12 +387,10 @@ def test_import_many():
     check_ast_roundtrip(import_many)
 
 
-@pytest.mark.skipif(not six.PY3, reason="Only for Python 3")
 def test_nonlocal():
     check_ast_roundtrip(nonlocal_ex)
 
 
-@pytest.mark.skipif(not six.PY3, reason="Only for Python 3")
 def test_raise_from():
     check_ast_roundtrip(raise_from)
 
@@ -449,17 +427,11 @@ def test_joined_str_361():
     check_ast_roundtrip('f"{key:4}={value!a:#06x}"')
 
 
-@pytest.mark.skipif(not six.PY2, reason="Only for Python 2")
-def test_repr():
-    check_ast_roundtrip(a_repr)
-
-
 @pytest.mark.skipif(sys.version_info[:2] < (3, 6), reason="Only for Python 3.6 or greater")
 def test_complex_f_string():
     check_ast_roundtrip(complex_f_string)
 
 
-@pytest.mark.skipif(not six.PY3, reason="Only for Python 3")
 def test_annotations():
     check_ast_roundtrip("def f(a : int): pass")
     check_ast_roundtrip("def f(a: int = 5): pass")
@@ -511,7 +483,6 @@ def test_class_decorators():
     check_ast_roundtrip(class_decorator)
 
 
-@pytest.mark.skipif(not six.PY3, reason="Only for Python 3")
 def test_class_definition():
     check_ast_roundtrip("class A(metaclass=type, *[], **{}): pass")
 
@@ -525,7 +496,6 @@ def test_try_except_finally():
     check_ast_roundtrip(try_except_finally)
 
 
-@pytest.mark.skipif(not six.PY3, reason="Only for Python 3")
 def test_starred_assignment():
     check_ast_roundtrip("a, *b, c = seq")
     check_ast_roundtrip("a, (*b, c) = seq")
diff --git a/lib/spack/spack/url.py b/lib/spack/spack/url.py
index 08eef72e93..972a964d25 100644
--- a/lib/spack/spack/url.py
+++ b/lib/spack/spack/url.py
@@ -25,11 +25,10 @@ This is useful if a user asks for a package at a particular version number;
 spack doesn't need anyone to tell it where to get the tarball even though
 it's never been told about that version before.
 """
+import io
 import os
 import re
-
-from six import StringIO
-from six.moves.urllib.parse import urlsplit, urlunsplit
+from urllib.parse import urlsplit, urlunsplit
 
 import llnl.util.tty as tty
 from llnl.util.tty.color import cescape, colorize
@@ -874,7 +873,7 @@ def color_url(path, **kwargs):
     vends = [vo + vl - 1 for vo in voffs]
 
     nerr = verr = 0
-    out = StringIO()
+    out = io.StringIO()
     for i in range(len(path)):
         if i == vs:
             out.write("@c")
diff --git a/lib/spack/spack/util/environment.py b/lib/spack/spack/util/environment.py
index 5f3fb7a61a..f46b2508e0 100644
--- a/lib/spack/spack/util/environment.py
+++ b/lib/spack/spack/util/environment.py
@@ -9,15 +9,13 @@ import inspect
 import json
 import os
 import os.path
+import pickle
 import platform
 import re
+import shlex
 import socket
 import sys
 
-import six
-from six.moves import cPickle
-from six.moves import shlex_quote as cmd_quote
-
 import llnl.util.tty as tty
 from llnl.util.lang import dedupe
 
@@ -131,7 +129,7 @@ def env_var_to_source_line(var, val):
             fname=bash_function_finder.sub(r"\1", var), decl=val
         )
     else:
-        source_line = "{var}={val}; export {var}".format(var=var, val=cmd_quote(val))
+        source_line = "{var}={val}; export {var}".format(var=var, val=shlex.quote(val))
     return source_line
 
 
@@ -154,7 +152,7 @@ def dump_environment(path, environment=None):
 @system_path_filter(arg_slice=slice(1))
 def pickle_environment(path, environment=None):
     """Pickle an environment dictionary to a file."""
-    cPickle.dump(dict(environment if environment else os.environ), open(path, "wb"), protocol=2)
+    pickle.dump(dict(environment if environment else os.environ), open(path, "wb"), protocol=2)
 
 
 def get_host_environment_metadata():
@@ -627,7 +625,7 @@ class EnvironmentModifications(object):
                     cmds += _shell_unset_strings[shell].format(name)
                 else:
                     if sys.platform != "win32":
-                        cmd = _shell_set_strings[shell].format(name, cmd_quote(new_env[name]))
+                        cmd = _shell_set_strings[shell].format(name, shlex.quote(new_env[name]))
                     else:
                         cmd = _shell_set_strings[shell].format(name, new_env[name])
                     cmds += cmd
@@ -1024,7 +1022,7 @@ def environment_after_sourcing_files(*files, **kwargs):
     current_environment = kwargs.get("env", dict(os.environ))
     for f in files:
         # Normalize the input to the helper function
-        if isinstance(f, six.string_types):
+        if isinstance(f, str):
             f = [f]
 
         current_environment = _source_single_file(f, environment=current_environment)
diff --git a/lib/spack/spack/util/executable.py b/lib/spack/spack/util/executable.py
index 6160b95266..e1e359ed0c 100644
--- a/lib/spack/spack/util/executable.py
+++ b/lib/spack/spack/util/executable.py
@@ -9,9 +9,6 @@ import shlex
 import subprocess
 import sys
 
-from six import string_types, text_type
-from six.moves import shlex_quote
-
 import llnl.util.tty as tty
 
 import spack.error
@@ -168,7 +165,7 @@ class Executable(object):
             raise ValueError("Cannot use `str` as input stream.")
 
         def streamify(arg, mode):
-            if isinstance(arg, string_types):
+            if isinstance(arg, str):
                 return open(arg, mode), True
             elif arg in (str, str.split):
                 return subprocess.PIPE, False
@@ -213,17 +210,17 @@ class Executable(object):
                 result = ""
                 if output in (str, str.split):
                     if sys.platform == "win32":
-                        outstr = text_type(out.decode("ISO-8859-1"))
+                        outstr = str(out.decode("ISO-8859-1"))
                     else:
-                        outstr = text_type(out.decode("utf-8"))
+                        outstr = str(out.decode("utf-8"))
                     result += outstr
                     if output is str.split:
                         sys.stdout.write(outstr)
                 if error in (str, str.split):
                     if sys.platform == "win32":
-                        errstr = text_type(err.decode("ISO-8859-1"))
+                        errstr = str(err.decode("ISO-8859-1"))
                     else:
-                        errstr = text_type(err.decode("utf-8"))
+                        errstr = str(err.decode("utf-8"))
                     result += errstr
                     if error is str.split:
                         sys.stderr.write(errstr)
@@ -283,7 +280,7 @@ def which_string(*args, **kwargs):
     path = kwargs.get("path", os.environ.get("PATH", ""))
     required = kwargs.get("required", False)
 
-    if isinstance(path, string_types):
+    if isinstance(path, str):
         path = path.split(os.pathsep)
 
     for name in args:
@@ -334,7 +331,7 @@ def which(*args, **kwargs):
         Executable: The first executable that is found in the path
     """
     exe = which_string(*args, **kwargs)
-    return Executable(shlex_quote(exe)) if exe else None
+    return Executable(shlex.quote(exe)) if exe else None
 
 
 class ProcessError(spack.error.SpackError):
diff --git a/lib/spack/spack/util/log_parse.py b/lib/spack/spack/util/log_parse.py
index e498a41bdf..a84a806aca 100644
--- a/lib/spack/spack/util/log_parse.py
+++ b/lib/spack/spack/util/log_parse.py
@@ -5,10 +5,10 @@
 
 from __future__ import print_function
 
+import io
 import sys
 
 from ctest_log_parser import BuildError, BuildWarning, CTestLogParser
-from six import StringIO
 
 import llnl.util.tty as tty
 from llnl.util.tty.color import cescape, colorize
@@ -86,7 +86,7 @@ def make_log_context(log_events, width=None):
         width = sys.maxsize
     wrap_width = width - num_width - 6
 
-    out = StringIO()
+    out = io.StringIO()
     next_line = 1
     for event in log_events:
         start = event.start
diff --git a/lib/spack/spack/util/naming.py b/lib/spack/spack/util/naming.py
index 46a2f3528c..b0a693738e 100644
--- a/lib/spack/spack/util/naming.py
+++ b/lib/spack/spack/util/naming.py
@@ -6,12 +6,11 @@
 # Need this because of spack.util.string
 from __future__ import absolute_import
 
+import io
 import itertools
 import re
 import string
 
-from six import StringIO
-
 import spack.error
 
 __all__ = [
@@ -261,6 +260,6 @@ class NamespaceTrie(object):
             stream.write(self._subspaces[name]._str_helper(stream, level + 1))
 
     def __str__(self):
-        stream = StringIO()
+        stream = io.StringIO()
         self._str_helper(stream)
         return stream.getvalue()
diff --git a/lib/spack/spack/util/path.py b/lib/spack/spack/util/path.py
index 49794429d3..2dc646418e 100644
--- a/lib/spack/spack/util/path.py
+++ b/lib/spack/spack/util/path.py
@@ -15,8 +15,7 @@ import subprocess
 import sys
 import tempfile
 from datetime import date
-
-from six.moves.urllib.parse import urlparse
+from urllib.parse import urlparse
 
 import llnl.util.tty as tty
 from llnl.util.lang import memoized
diff --git a/lib/spack/spack/util/py2.py b/lib/spack/spack/util/py2.py
deleted file mode 100644
index b92a6d66d9..0000000000
--- a/lib/spack/spack/util/py2.py
+++ /dev/null
@@ -1,16 +0,0 @@
-# Copyright 2013-2022 Lawrence Livermore National Security, LLC and other
-# Spack Project Developers. See the top-level COPYRIGHT file for details.
-#
-# SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-import base64
-
-from six import PY3, binary_type, text_type
-
-
-def b32encode(digest):
-    # type: (binary_type) -> text_type
-    b32 = base64.b32encode(digest)
-    if PY3:
-        return b32.decode()
-    return b32
diff --git a/lib/spack/spack/util/s3.py b/lib/spack/spack/util/s3.py
index 9945ae5e5f..06eeab3936 100644
--- a/lib/spack/spack/util/s3.py
+++ b/lib/spack/spack/util/s3.py
@@ -2,10 +2,8 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
 import os
-
-import six.moves.urllib.parse as urllib_parse
+import urllib.parse
 
 import spack
 import spack.util.url as url_util
@@ -30,7 +28,7 @@ def get_mirror_connection(url, url_type="push"):
 
 
 def _parse_s3_endpoint_url(endpoint_url):
-    if not urllib_parse.urlparse(endpoint_url, scheme="").scheme:
+    if not urllib.parse.urlparse(endpoint_url, scheme="").scheme:
         endpoint_url = "://".join(("https", endpoint_url))
 
     return endpoint_url
diff --git a/lib/spack/spack/util/spack_json.py b/lib/spack/spack/util/spack_json.py
index 305af820aa..a6bef3ea0d 100644
--- a/lib/spack/spack/util/spack_json.py
+++ b/lib/spack/spack/util/spack_json.py
@@ -4,12 +4,9 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 """Simple wrapper around JSON to guarantee consistent use of load/dump. """
-import collections
 import json
 from typing import Any, Dict, Optional  # novm
 
-from six import PY3, iteritems, string_types
-
 import spack.error
 
 __all__ = ["load", "dump", "SpackJSONError", "encode_json_dict", "decode_json_dict"]
@@ -20,7 +17,7 @@ _json_dump_args = {"indent": 2, "separators": (",", ": ")}
 def load(stream):
     # type: (Any) -> Dict
     """Spack JSON needs to be ordered to support specs."""
-    if isinstance(stream, string_types):
+    if isinstance(stream, str):
         load = json.loads  # type: ignore[assignment]
     else:
         load = json.load  # type: ignore[assignment]
@@ -56,26 +53,6 @@ def _strify(data, ignore_dicts=False):
 
     Converts python 2 unicodes to str in JSON data, or the other way around."""
     # this is a no-op in python 3
-    if PY3:
-        return data
-
-    # if this is a unicode string in python 2, return its string representation
-    if isinstance(data, string_types):
-        return data.encode("utf-8")
-
-    # if this is a list of values, return list of byteified values
-    if isinstance(data, list):
-        return [_strify(item, ignore_dicts=True) for item in data]
-
-    # if this is a dictionary, return dictionary of byteified keys and values
-    # but only if we haven't already byteified it
-    if isinstance(data, dict) and not ignore_dicts:
-        return collections.OrderedDict(
-            (_strify(key, ignore_dicts=True), _strify(value, ignore_dicts=True))
-            for key, value in iteritems(data)
-        )
-
-    # if it's anything else, return it in its original form
     return data
 
 
diff --git a/lib/spack/spack/util/spack_yaml.py b/lib/spack/spack/util/spack_yaml.py
index 88bd4b45a6..6e27adee1c 100644
--- a/lib/spack/spack/util/spack_yaml.py
+++ b/lib/spack/spack/util/spack_yaml.py
@@ -15,12 +15,12 @@
 import collections
 import collections.abc
 import ctypes
+import io
 import re
 from typing import List  # novm
 
 import ruamel.yaml as yaml
 from ruamel.yaml import RoundTripDumper, RoundTripLoader
-from six import StringIO, string_types
 
 from llnl.util.tty.color import cextra, clen, colorize
 
@@ -52,7 +52,7 @@ class syaml_int(int):
 
 #: mapping from syaml type -> primitive type
 syaml_types = {
-    syaml_str: string_types,
+    syaml_str: str,
     syaml_int: int,
     syaml_dict: dict,
     syaml_list: list,
@@ -263,7 +263,7 @@ class LineAnnotationDumper(OrderedLineDumper):
         result = super(LineAnnotationDumper, self).represent_data(data)
         if data is None:
             result.value = syaml_str("null")
-        elif isinstance(result.value, string_types):
+        elif isinstance(result.value, str):
             result.value = syaml_str(data)
         if markable(result.value):
             mark(result.value, data)
@@ -318,7 +318,7 @@ def dump_config(*args, **kwargs):
 def dump_annotated(data, stream=None, *args, **kwargs):
     kwargs["Dumper"] = LineAnnotationDumper
 
-    sio = StringIO()
+    sio = io.StringIO()
     yaml.dump(data, sio, *args, **kwargs)
 
     # write_line_break() is not called by YAML for empty lines, so we
@@ -327,7 +327,7 @@ def dump_annotated(data, stream=None, *args, **kwargs):
 
     getvalue = None
     if stream is None:
-        stream = StringIO()
+        stream = io.StringIO()
         getvalue = stream.getvalue
 
     # write out annotations and lines, accounting for color
diff --git a/lib/spack/spack/util/unparse/__init__.py b/lib/spack/spack/util/unparse/__init__.py
index 3469443105..73f7d106c6 100644
--- a/lib/spack/spack/util/unparse/__init__.py
+++ b/lib/spack/spack/util/unparse/__init__.py
@@ -2,10 +2,9 @@
 #
 # SPDX-License-Identifier: Python-2.0
 # coding: utf-8
-
 from __future__ import absolute_import
 
-from six.moves import cStringIO
+import io
 
 from .unparser import Unparser
 
@@ -13,7 +12,6 @@ __version__ = "1.6.3"
 
 
 def unparse(tree, py_ver_consistent=False):
-    v = cStringIO()
-    unparser = Unparser(py_ver_consistent=py_ver_consistent)
-    unparser.visit(tree, v)
+    v = io.StringIO()
+    Unparser(py_ver_consistent=py_ver_consistent).visit(tree, v)
     return v.getvalue().strip() + "\n"
diff --git a/lib/spack/spack/util/unparse/unparser.py b/lib/spack/spack/util/unparse/unparser.py
index c204aea25a..c24cf8ee1a 100644
--- a/lib/spack/spack/util/unparse/unparser.py
+++ b/lib/spack/spack/util/unparse/unparser.py
@@ -1,16 +1,13 @@
 # Copyright (c) 2014-2021, Simon Percivall and Spack Project Developers.
 #
 # SPDX-License-Identifier: Python-2.0
-
 "Usage: unparse.py <path to source file>"
 from __future__ import print_function, unicode_literals
 
 import ast
 import sys
 from contextlib import contextmanager
-
-import six
-from six import StringIO
+from io import StringIO
 
 
 # TODO: if we require Python 3.7, use its `nullcontext()`
@@ -76,11 +73,7 @@ def is_simple_tuple(slice_value):
     return (
         isinstance(slice_value, ast.Tuple)
         and slice_value.elts
-        and (
-            # Python 2 doesn't allow starred elements in tuples like Python 3
-            six.PY2
-            or not any(isinstance(elt, ast.Starred) for elt in slice_value.elts)
-        )
+        and not any(isinstance(elt, ast.Starred) for elt in slice_value.elts)
     )
 
 
@@ -145,7 +138,7 @@ class Unparser:
 
     def write(self, text):
         "Append a piece of text to the current line."
-        self.f.write(six.text_type(text))
+        self.f.write(str(text))
 
     class _Block:
         """A context manager for preparing the source for blocks. It adds
@@ -395,25 +388,14 @@ class Unparser:
 
     def visit_Raise(self, node):
         self.fill("raise")
-        if six.PY3:
-            if not node.exc:
-                assert not node.cause
-                return
-            self.write(" ")
-            self.dispatch(node.exc)
-            if node.cause:
-                self.write(" from ")
-                self.dispatch(node.cause)
-        else:
-            self.write(" ")
-            if node.type:
-                self.dispatch(node.type)
-            if node.inst:
-                self.write(", ")
-                self.dispatch(node.inst)
-            if node.tback:
-                self.write(", ")
-                self.dispatch(node.tback)
+        if not node.exc:
+            assert not node.cause
+            return
+        self.write(" ")
+        self.dispatch(node.exc)
+        if node.cause:
+            self.write(" from ")
+            self.dispatch(node.cause)
 
     def visit_Try(self, node):
         self.fill("try")
@@ -462,10 +444,7 @@ class Unparser:
             self.dispatch(node.type)
         if node.name:
             self.write(" as ")
-            if six.PY3:
-                self.write(node.name)
-            else:
-                self.dispatch(node.name)
+            self.write(node.name)
         with self.block():
             self.dispatch(node.body)
 
@@ -475,42 +454,35 @@ class Unparser:
             self.fill("@")
             self.dispatch(deco)
         self.fill("class " + node.name)
-        if six.PY3:
-            with self.delimit_if("(", ")", condition=node.bases or node.keywords):
-                comma = False
-                for e in node.bases:
+        with self.delimit_if("(", ")", condition=node.bases or node.keywords):
+            comma = False
+            for e in node.bases:
+                if comma:
+                    self.write(", ")
+                else:
+                    comma = True
+                self.dispatch(e)
+            for e in node.keywords:
+                if comma:
+                    self.write(", ")
+                else:
+                    comma = True
+                self.dispatch(e)
+            if sys.version_info[:2] < (3, 5):
+                if node.starargs:
                     if comma:
                         self.write(", ")
                     else:
                         comma = True
-                    self.dispatch(e)
-                for e in node.keywords:
+                    self.write("*")
+                    self.dispatch(node.starargs)
+                if node.kwargs:
                     if comma:
                         self.write(", ")
                     else:
                         comma = True
-                    self.dispatch(e)
-                if sys.version_info[:2] < (3, 5):
-                    if node.starargs:
-                        if comma:
-                            self.write(", ")
-                        else:
-                            comma = True
-                        self.write("*")
-                        self.dispatch(node.starargs)
-                    if node.kwargs:
-                        if comma:
-                            self.write(", ")
-                        else:
-                            comma = True
-                        self.write("**")
-                        self.dispatch(node.kwargs)
-        elif node.bases:
-            with self.delimit("(", ")"):
-                for a in node.bases[:-1]:
-                    self.dispatch(a)
-                    self.write(", ")
-                self.dispatch(node.bases[-1])
+                    self.write("**")
+                    self.dispatch(node.kwargs)
         with self.block():
             self.dispatch(node.body)
 
@@ -654,26 +626,11 @@ class Unparser:
         self.write(repr(node.s))
 
     def visit_Str(self, tree):
-        if six.PY3:
-            # Python 3.5, 3.6, and 3.7 can't tell if something was written as a
-            # unicode constant. Try to make that consistent with 'u' for '\u- literals
-            if self._py_ver_consistent and repr(tree.s).startswith("'\\u"):
-                self.write("u")
-            self._write_constant(tree.s)
-        elif self._py_ver_consistent:
-            self.write(repr(tree.s))  # just do a python 2 repr for consistency
-        else:
-            # if from __future__ import unicode_literals is in effect,
-            # then we want to output string literals using a 'b' prefix
-            # and unicode literals with no prefix.
-            if "unicode_literals" not in self.future_imports:
-                self.write(repr(tree.s))
-            elif isinstance(tree.s, str):
-                self.write("b" + repr(tree.s))
-            elif isinstance(tree.s, unicode):  # noqa: F821
-                self.write(repr(tree.s).lstrip("u"))
-            else:
-                assert False, "shouldn't get here"
+        # Python 3.5, 3.6, and 3.7 can't tell if something was written as a
+        # unicode constant. Try to make that consistent with 'u' for '\u- literals
+        if self._py_ver_consistent and repr(tree.s).startswith("'\\u"):
+            self.write("u")
+        self._write_constant(tree.s)
 
     def visit_JoinedStr(self, node):
         # JoinedStr(expr* values)
@@ -805,15 +762,7 @@ class Unparser:
 
     def visit_Num(self, node):
         repr_n = repr(node.n)
-        if six.PY3:
-            self.write(repr_n.replace("inf", INFSTR))
-        else:
-            # Parenthesize negative numbers, to avoid turning (-1)**2 into -1**2.
-            with self.require_parens(pnext(_Precedence.FACTOR), node):
-                if "inf" in repr_n and repr_n.endswith("*j"):
-                    repr_n = repr_n.replace("*j", "j")
-                # Substitute overflowing decimal literal for AST infinities.
-                self.write(repr_n.replace("inf", INFSTR))
+        self.write(repr_n.replace("inf", INFSTR))
 
     def visit_List(self, node):
         with self.delimit("[", "]"):
@@ -917,17 +866,7 @@ class Unparser:
             if operator_precedence != _Precedence.FACTOR:
                 self.write(" ")
             self.set_precedence(operator_precedence, node.operand)
-
-            if six.PY2 and isinstance(node.op, ast.USub) and isinstance(node.operand, ast.Num):
-                # If we're applying unary minus to a number, parenthesize the number.
-                # This is necessary: -2147483648 is different from -(2147483648) on
-                # a 32-bit machine (the first is an int, the second a long), and
-                # -7j is different from -(7j).  (The first has real part 0.0, the second
-                # has real part -0.0.)
-                with self.delimit("(", ")"):
-                    self.dispatch(node.operand)
-            else:
-                self.dispatch(node.operand)
+            self.dispatch(node.operand)
 
     binop = {
         "Add": "+",
diff --git a/lib/spack/spack/util/url.py b/lib/spack/spack/util/url.py
index c9c7343585..d0f9ef7393 100644
--- a/lib/spack/spack/util/url.py
+++ b/lib/spack/spack/util/url.py
@@ -11,9 +11,7 @@ import itertools
 import posixpath
 import re
 import sys
-
-import six.moves.urllib.parse
-from six import string_types
+import urllib.parse
 
 from spack.util.path import (
     canonicalize_path,
@@ -50,7 +48,7 @@ def local_file_path(url):
     If url is a file:// URL, return the absolute path to the local
     file or directory referenced by it.  Otherwise, return None.
     """
-    if isinstance(url, string_types):
+    if isinstance(url, str):
         url = parse(url)
 
     if url.scheme == "file":
@@ -75,23 +73,23 @@ def parse(url, scheme="file"):
         url (str): URL to be parsed
         scheme (str): associated URL scheme
     Returns:
-        (six.moves.urllib.parse.ParseResult): For file scheme URLs, the
+        (urllib.parse.ParseResult): For file scheme URLs, the
         netloc and path components are concatenated and passed through
         spack.util.path.canoncalize_path().  Otherwise, the returned value
         is the same as urllib's urlparse() with allow_fragments=False.
     """
     # guarantee a value passed in is of proper url format. Guarantee
     # allows for easier string manipulation accross platforms
-    if isinstance(url, string_types):
+    if isinstance(url, str):
         require_url_format(url)
         url = escape_file_url(url)
     url_obj = (
-        six.moves.urllib.parse.urlparse(
+        urllib.parse.urlparse(
             url,
             scheme=scheme,
             allow_fragments=False,
         )
-        if isinstance(url, string_types)
+        if isinstance(url, str)
         else url
     )
 
@@ -119,7 +117,7 @@ def parse(url, scheme="file"):
     if sys.platform == "win32":
         path = convert_to_posix_path(path)
 
-    return six.moves.urllib.parse.ParseResult(
+    return urllib.parse.ParseResult(
         scheme=scheme,
         netloc=netloc,
         path=path,
@@ -134,7 +132,7 @@ def format(parsed_url):
 
     Returns a canonicalized format of the given URL as a string.
     """
-    if isinstance(parsed_url, string_types):
+    if isinstance(parsed_url, str):
         parsed_url = parse(parsed_url)
 
     return parsed_url.geturl()
@@ -195,8 +193,7 @@ def join(base_url, path, *extra, **kwargs):
       'file:///opt/spack'
     """
     paths = [
-        (x) if isinstance(x, string_types) else x.geturl()
-        for x in itertools.chain((base_url, path), extra)
+        (x) if isinstance(x, str) else x.geturl() for x in itertools.chain((base_url, path), extra)
     ]
 
     paths = [convert_to_posix_path(x) for x in paths]
@@ -204,7 +201,7 @@ def join(base_url, path, *extra, **kwargs):
     last_abs_component = None
     scheme = ""
     for i in range(n - 1, -1, -1):
-        obj = six.moves.urllib.parse.urlparse(
+        obj = urllib.parse.urlparse(
             paths[i],
             scheme="",
             allow_fragments=False,
@@ -218,7 +215,7 @@ def join(base_url, path, *extra, **kwargs):
                 # Without a scheme, we have to go back looking for the
                 # next-last component that specifies a scheme.
                 for j in range(i - 1, -1, -1):
-                    obj = six.moves.urllib.parse.urlparse(
+                    obj = urllib.parse.urlparse(
                         paths[j],
                         scheme="",
                         allow_fragments=False,
@@ -238,7 +235,7 @@ def join(base_url, path, *extra, **kwargs):
     if last_abs_component is not None:
         paths = paths[last_abs_component:]
         if len(paths) == 1:
-            result = six.moves.urllib.parse.urlparse(
+            result = urllib.parse.urlparse(
                 paths[0],
                 scheme="file",
                 allow_fragments=False,
@@ -248,7 +245,7 @@ def join(base_url, path, *extra, **kwargs):
             # file:// URL component with a relative path, the relative path
             # needs to be resolved.
             if result.scheme == "file" and result.netloc:
-                result = six.moves.urllib.parse.ParseResult(
+                result = urllib.parse.ParseResult(
                     scheme=result.scheme,
                     netloc="",
                     path=posixpath.abspath(result.netloc + result.path),
@@ -306,7 +303,7 @@ def _join(base_url, path, *extra, **kwargs):
         base_path = convert_to_posix_path(base_path)
 
     return format(
-        six.moves.urllib.parse.ParseResult(
+        urllib.parse.ParseResult(
             scheme=scheme,
             netloc=netloc,
             path=base_path,
diff --git a/lib/spack/spack/util/web.py b/lib/spack/spack/util/web.py
index 9d8588c2b9..543bb43c5c 100644
--- a/lib/spack/spack/util/web.py
+++ b/lib/spack/spack/util/web.py
@@ -16,10 +16,8 @@ import ssl
 import sys
 import traceback
 from html.parser import HTMLParser
-
-import six
-from six.moves.urllib.error import URLError
-from six.moves.urllib.request import Request, urlopen
+from urllib.error import URLError
+from urllib.request import Request, urlopen
 
 import llnl.util.lang
 import llnl.util.tty as tty
@@ -683,7 +681,7 @@ def spider(root_urls, depth=0, concurrency=32):
 
         return pages, links, subcalls
 
-    if isinstance(root_urls, six.string_types):
+    if isinstance(root_urls, str):
         root_urls = [root_urls]
 
     # Clear the local cache of visited pages before starting the search
diff --git a/lib/spack/spack/variant.py b/lib/spack/spack/variant.py
index b006ae985e..1e646fa3b4 100644
--- a/lib/spack/spack/variant.py
+++ b/lib/spack/spack/variant.py
@@ -9,12 +9,10 @@ variants both in packages and in specs.
 import collections.abc
 import functools
 import inspect
+import io
 import itertools
 import re
 
-import six
-from six import StringIO
-
 import llnl.util.lang as lang
 import llnl.util.tty.color
 
@@ -665,7 +663,7 @@ class VariantMap(lang.HashableMap):
             bool_keys.append(key) if isinstance(self[key].value, bool) else kv_keys.append(key)
 
         # add spaces before and after key/value variants.
-        string = StringIO()
+        string = io.StringIO()
 
         for key in bool_keys:
             string.write(str(self[key]))
@@ -895,12 +893,12 @@ class Value(object):
         return hash(self.value)
 
     def __eq__(self, other):
-        if isinstance(other, (six.string_types, bool)):
+        if isinstance(other, (str, bool)):
             return self.value == other
         return self.value == other.value
 
     def __lt__(self, other):
-        if isinstance(other, six.string_types):
+        if isinstance(other, str):
             return self.value < other
         return self.value < other.value
 
diff --git a/lib/spack/spack/verify.py b/lib/spack/spack/verify.py
index e18c98373d..82e187dd47 100644
--- a/lib/spack/spack/verify.py
+++ b/lib/spack/spack/verify.py
@@ -2,6 +2,7 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import base64
 import hashlib
 import os
 
@@ -10,14 +11,14 @@ import llnl.util.tty as tty
 import spack.filesystem_view
 import spack.store
 import spack.util.file_permissions as fp
-import spack.util.py2 as compat
 import spack.util.spack_json as sjson
 
 
 def compute_hash(path):
     with open(path, "rb") as f:
         sha1 = hashlib.sha1(f.read()).digest()
-        return compat.b32encode(sha1)
+        b32 = base64.b32encode(sha1)
+        return b32.decode()
 
 
 def create_manifest_entry(path):
diff --git a/lib/spack/spack/version.py b/lib/spack/spack/version.py
index f4f08d8c77..20f0c13d1c 100644
--- a/lib/spack/spack/version.py
+++ b/lib/spack/spack/version.py
@@ -30,8 +30,6 @@ import re
 from bisect import bisect_left
 from functools import wraps
 
-from six import string_types
-
 import llnl.util.tty as tty
 from llnl.util.filesystem import mkdirp, working_dir
 
@@ -721,9 +719,9 @@ class GitVersion(VersionBase):
 
 class VersionRange(object):
     def __init__(self, start, end):
-        if isinstance(start, string_types):
+        if isinstance(start, str):
             start = Version(start)
-        if isinstance(end, string_types):
+        if isinstance(end, str):
             end = Version(end)
 
         self.start = start
@@ -939,7 +937,7 @@ class VersionList(object):
     def __init__(self, vlist=None):
         self.versions = []
         if vlist is not None:
-            if isinstance(vlist, string_types):
+            if isinstance(vlist, str):
                 vlist = _string_to_version(vlist)
                 if type(vlist) == VersionList:
                     self.versions = vlist.versions
@@ -1193,7 +1191,7 @@ def ver(obj):
     """
     if isinstance(obj, (list, tuple)):
         return VersionList(obj)
-    elif isinstance(obj, string_types):
+    elif isinstance(obj, str):
         return _string_to_version(obj)
     elif isinstance(obj, (int, float)):
         return _string_to_version(str(obj))