Convert Python 2 idioms to Python 2/3-compatible ones.

- convert print, StringIO, except as, octals, izip
- convert print statement to print function
- convert StringIO to six.StringIO
  - remove usage of csv reader in Spec, in favor of simple regex
  - csv reader only does byte strings
- convert 0755 octal literals to 0o755
- convert `except Foo, e` to `except Foo as e`
- fix a few places `str` is used.
  - may need to switch everything to str later.
- convert iteritems usages to use six.iteritems
- fix urllib and HTMLParser
- port metaclasses to use six.with_metaclass
- More octal literal conversions for Python 2/3
- Fix a new octal literal.
- Convert `basestring` to `six.string_types`
- Convert xrange -> range
- Fix various issues with encoding, iteritems, and Python3 semantics.
- Convert contextlib.nested to explicitly nexted context managers.
- Convert use of filter() to list comprehensions.
- Replace reduce() with list comprehensions.
-  Clean up composite: replace inspect.ismethod() with callable()
- Python 3 doesn't have "method" objects; inspect.ismethod returns False.
- Need to use callable in Composite to make it work.
- Update colify to use future division.
- Fix zip() usages that need to be lists.
- Python3: Use line-buffered logging instead of unbuffered.
- Python3 raises an error with unbuffered I/O
  - See https://bugs.python.org/issue17404

74 files changed, 396 insertions, 323 deletions

diff --git a/bin/spack b/bin/spack
index 550b999eb9..f33d219b8b 100755
--- a/bin/spack
+++ b/bin/spack
@@ -24,6 +24,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import sys
 if (sys.version_info[0] > 2) or (sys.version_info[:2] < (2, 6)):
     v_info = sys.version_info[:3]
@@ -74,8 +76,8 @@ for pyc_file in orphaned_pyc_files:
     try:
         os.remove(pyc_file)
     except OSError as e:
-        print ("WARNING: Spack may fail mysteriously. "
-               "Couldn't remove orphaned .pyc file: %s" % pyc_file)
+        print("WARNING: Spack may fail mysteriously. "
+              "Couldn't remove orphaned .pyc file: %s" % pyc_file)
 
 # If there is no working directory, use the spack prefix.
 try:
diff --git a/lib/spack/llnl/util/filesystem.py b/lib/spack/llnl/util/filesystem.py
index f456a5edf1..8922010e70 100644
--- a/lib/spack/llnl/util/filesystem.py
+++ b/lib/spack/llnl/util/filesystem.py
@@ -175,9 +175,9 @@ def change_sed_delimiter(old_delim, new_delim, *filenames):
 def set_install_permissions(path):
     """Set appropriate permissions on the installed file."""
     if os.path.isdir(path):
-        os.chmod(path, 0755)
+        os.chmod(path, 0o755)
     else:
-        os.chmod(path, 0644)
+        os.chmod(path, 0o644)
 
 
 def copy_mode(src, dest):
diff --git a/lib/spack/llnl/util/lang.py b/lib/spack/llnl/util/lang.py
index d9fef42e53..ad62063061 100644
--- a/lib/spack/llnl/util/lang.py
+++ b/lib/spack/llnl/util/lang.py
@@ -27,6 +27,7 @@ import re
 import functools
 import collections
 import inspect
+from six import string_types
 
 # Ignore emacs backups when listing modules
 ignore_modules = [r'^\.#', '~$']
@@ -80,7 +81,7 @@ def index_by(objects, *funcs):
         return objects
 
     f = funcs[0]
-    if isinstance(f, basestring):
+    if isinstance(f, str):
         f = lambda x: getattr(x, funcs[0])
     elif isinstance(f, tuple):
         f = lambda x: tuple(getattr(x, p) for p in funcs[0])
@@ -326,7 +327,7 @@ def match_predicate(*args):
     """
     def match(string):
         for arg in args:
-            if isinstance(arg, basestring):
+            if isinstance(arg, string_types):
                 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 f73d96a4e4..f78d889037 100644
--- a/lib/spack/llnl/util/tty/__init__.py
+++ b/lib/spack/llnl/util/tty/__init__.py
@@ -29,7 +29,7 @@ import fcntl
 import termios
 import struct
 import traceback
-from StringIO import StringIO
+from six import StringIO
 
 from llnl.util.tty.color import *
 
@@ -93,7 +93,7 @@ def msg(message, *args, **kwargs):
     else:
         cwrite("@*b{%s==>} %s" % (st_text, cescape(message)))
     for arg in args:
-        print indent + str(arg)
+        print(indent + str(arg))
 
 
 def info(message, *args, **kwargs):
@@ -201,7 +201,7 @@ def get_yes_or_no(prompt, **kwargs):
         if not ans:
             result = default_value
             if result is None:
-                print "Please enter yes or no."
+                print("Please enter yes or no.")
         else:
             if ans == 'y' or ans == 'yes':
                 result = True
@@ -239,7 +239,7 @@ def hline(label=None, **kwargs):
     out.write(label)
     out.write(suffix)
 
-    print out.getvalue()
+    print(out.getvalue())
 
 
 def terminal_size():
diff --git a/lib/spack/llnl/util/tty/colify.py b/lib/spack/llnl/util/tty/colify.py
index 67acdfa517..83de530ef1 100644
--- a/lib/spack/llnl/util/tty/colify.py
+++ b/lib/spack/llnl/util/tty/colify.py
@@ -25,9 +25,11 @@
 """
 Routines for printing columnar output.  See colify() for more information.
 """
+from __future__ import division
+
 import os
 import sys
-from StringIO import StringIO
+from six import StringIO
 
 from llnl.util.tty import terminal_size
 from llnl.util.tty.color import clen, cextra
@@ -64,18 +66,18 @@ def config_variable_cols(elts, console_width, padding, cols=0):
     # Get a bound on the most columns we could possibly have.
     # 'clen' ignores length of ansi color sequences.
     lengths = [clen(e) for e in elts]
-    max_cols = max(1, console_width / (min(lengths) + padding))
+    max_cols = max(1, console_width // (min(lengths) + padding))
     max_cols = min(len(elts), max_cols)
 
     # Range of column counts to try.  If forced, use the supplied value.
-    col_range = [cols] if cols else xrange(1, max_cols + 1)
+    col_range = [cols] if cols else range(1, max_cols + 1)
 
     # Determine the most columns possible for the console width.
     configs = [ColumnConfig(c) for c in col_range]
     for i, length in enumerate(lengths):
         for conf in configs:
             if conf.valid:
-                col = i / ((len(elts) + conf.cols - 1) / conf.cols)
+                col = i // ((len(elts) + conf.cols - 1) // conf.cols)
                 p = padding if col < (conf.cols - 1) else 0
 
                 if conf.widths[col] < (length + p):
@@ -107,7 +109,7 @@ def config_uniform_cols(elts, console_width, padding, cols=0):
     # 'clen' ignores length of ansi color sequences.
     max_len = max(clen(e) for e in elts) + padding
     if cols == 0:
-        cols = max(1, console_width / max_len)
+        cols = max(1, console_width // max_len)
         cols = min(len(elts), cols)
 
     config = ColumnConfig(cols)
@@ -193,12 +195,12 @@ def colify(elts, **options):
         raise ValueError("method must be one of: " + allowed_methods)
 
     cols = config.cols
-    rows = (len(elts) + cols - 1) / cols
+    rows = (len(elts) + cols - 1) // cols
     rows_last_col = len(elts) % rows
 
-    for row in xrange(rows):
+    for row in range(rows):
         output.write(" " * indent)
-        for col in xrange(cols):
+        for col in range(cols):
             elt = col * rows + row
             width = config.widths[col] + cextra(elts[elt])
             if col < cols - 1:
@@ -233,7 +235,7 @@ def colify_table(table, **options):
     columns = len(table[0])
 
     def transpose():
-        for i in xrange(columns):
+        for i in range(columns):
             for row in table:
                 yield row[i]
 
diff --git a/lib/spack/llnl/util/tty/log.py b/lib/spack/llnl/util/tty/log.py
index b1d45214ab..50e07c0b97 100644
--- a/lib/spack/llnl/util/tty/log.py
+++ b/lib/spack/llnl/util/tty/log.py
@@ -165,8 +165,12 @@ class log_output(object):
         self.p.join(60.0)  # 1 minute to join the child
 
     def _spawn_writing_daemon(self, read, input_stream):
-        # Parent: read from child, skip the with block.
-        read_file = os.fdopen(read, 'r', 0)
+        # This is the Parent: read from child, skip the with block.
+
+        # Use line buffering (3rd param = 1) since Python 3 has a bug
+        # that prevents unbuffered text I/O.
+        read_file = os.fdopen(read, 'r', 1)
+
         with open(self.filename, 'w') as log_file:
             with keyboard_input(input_stream):
                 while True:
diff --git a/lib/spack/spack/__init__.py b/lib/spack/spack/__init__.py
index b0f2faed76..b522804d8d 100644
--- a/lib/spack/spack/__init__.py
+++ b/lib/spack/spack/__init__.py
@@ -96,7 +96,7 @@ spack_version = Version("0.10.0")
 try:
     repo = spack.repository.RepoPath()
     sys.meta_path.append(repo)
-except spack.error.SpackError, e:
+except spack.error.SpackError as e:
     tty.die('while initializing Spack RepoPath:', e.message)
 
 
diff --git a/lib/spack/spack/architecture.py b/lib/spack/spack/architecture.py
index e44e0dc109..bace3c49f6 100644
--- a/lib/spack/spack/architecture.py
+++ b/lib/spack/spack/architecture.py
@@ -287,7 +287,7 @@ class OperatingSystem(object):
 
         # ensure all the version calls we made are cached in the parent
         # process, as well.  This speeds up Spack a lot.
-        clist = reduce(lambda x, y: x + y, compiler_lists)
+        clist = [comp for cl in compiler_lists for comp in cl]
         return clist
 
     def find_compiler(self, cmp_cls, *path):
diff --git a/lib/spack/spack/build_environment.py b/lib/spack/spack/build_environment.py
index 3e6dc12b35..a20a7b4db8 100644
--- a/lib/spack/spack/build_environment.py
+++ b/lib/spack/spack/build_environment.py
@@ -57,6 +57,7 @@ import os
 import shutil
 import sys
 import traceback
+from six import iteritems
 
 import llnl.util.lang as lang
 import llnl.util.tty as tty
@@ -310,7 +311,7 @@ def set_build_environment_variables(pkg, env, dirty=False):
     environment = compiler.environment
     if 'set' in environment:
         env_to_set = environment['set']
-        for key, value in env_to_set.iteritems():
+        for key, value in iteritems(env_to_set):
             env.set('SPACK_ENV_SET_%s' % key, value)
             env.set('%s' % key, value)
         # Let shell know which variables to set
@@ -322,8 +323,9 @@ def set_build_environment_variables(pkg, env, dirty=False):
         env.set('SPACK_COMPILER_EXTRA_RPATHS', extra_rpaths)
 
     # Add bin directories from dependencies to the PATH for the build.
-    bin_dirs = reversed(filter(os.path.isdir, [
-        '%s/bin' % d.prefix for d in pkg.spec.dependencies(deptype='build')]))
+    bin_dirs = reversed(
+        [d.prefix.bin for d in pkg.spec.dependencies(deptype='build')
+         if os.path.isdir(d.prefix.bin)])
     bin_dirs = filter_system_bin_paths(bin_dirs)
     for item in bin_dirs:
         env.prepend_path('PATH', item)
diff --git a/lib/spack/spack/build_systems/autotools.py b/lib/spack/spack/build_systems/autotools.py
index 76dfd0d16f..ffd00e7f69 100644
--- a/lib/spack/spack/build_systems/autotools.py
+++ b/lib/spack/spack/build_systems/autotools.py
@@ -146,7 +146,7 @@ class AutotoolsPackage(PackageBase):
         if config_guess is not None:
             try:
                 check_call([config_guess], stdout=PIPE, stderr=PIPE)
-                mod = stat(my_config_guess).st_mode & 0777 | S_IWUSR
+                mod = stat(my_config_guess).st_mode & 0o777 | S_IWUSR
                 os.chmod(my_config_guess, mod)
                 shutil.copyfile(config_guess, my_config_guess)
                 return True
diff --git a/lib/spack/spack/cmd/__init__.py b/lib/spack/spack/cmd/__init__.py
index 3a42510245..622ef4d96c 100644
--- a/lib/spack/spack/cmd/__init__.py
+++ b/lib/spack/spack/cmd/__init__.py
@@ -22,6 +22,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import os
 import re
 import sys
@@ -186,7 +188,7 @@ def display_specs(specs, **kwargs):
     # Traverse the index and print out each package
     for i, (architecture, compiler) in enumerate(sorted(index)):
         if i > 0:
-            print
+            print()
 
         header = "%s{%s} / %s{%s}" % (spack.spec.architecture_color,
                                       architecture, spack.spec.compiler_color,
@@ -205,7 +207,7 @@ def display_specs(specs, **kwargs):
 
             for abbrv, spec in zip(abbreviated, specs):
                 prefix = gray_hash(spec, hlen) if hashes else ''
-                print prefix + (format % (abbrv, spec.prefix))
+                print(prefix + (format % (abbrv, spec.prefix)))
 
         elif mode == 'deps':
             for spec in specs:
diff --git a/lib/spack/spack/cmd/arch.py b/lib/spack/spack/cmd/arch.py
index 5b9daf9dea..1079e7f215 100644
--- a/lib/spack/spack/cmd/arch.py
+++ b/lib/spack/spack/cmd/arch.py
@@ -22,6 +22,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import spack.architecture as architecture
 
 description = "print architecture information about this machine"
@@ -36,6 +38,6 @@ def setup_parser(subparser):
 
 def arch(parser, args):
     if args.platform:
-        print architecture.platform()
+        print(architecture.platform())
     else:
-        print architecture.sys_type()
+        print(architecture.sys_type())
diff --git a/lib/spack/spack/cmd/common/arguments.py b/lib/spack/spack/cmd/common/arguments.py
index a8bdcf692f..3115501439 100644
--- a/lib/spack/spack/cmd/common/arguments.py
+++ b/lib/spack/spack/cmd/common/arguments.py
@@ -81,7 +81,7 @@ _arguments['constraint'] = Args(
 _arguments['module_type'] = Args(
     '-m', '--module-type',
     choices=spack.modules.module_types.keys(),
-    default=spack.modules.module_types.keys()[0],
+    default=list(spack.modules.module_types.keys())[0],
     help='type of module files [default: %(default)s]')
 
 _arguments['yes_to_all'] = Args(
diff --git a/lib/spack/spack/cmd/compiler.py b/lib/spack/spack/cmd/compiler.py
index 22f3b3f26a..6067d44c5e 100644
--- a/lib/spack/spack/cmd/compiler.py
+++ b/lib/spack/spack/cmd/compiler.py
@@ -22,8 +22,11 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import argparse
 import sys
+from six import iteritems
 
 import llnl.util.tty as tty
 import spack.compilers
@@ -142,36 +145,36 @@ def compiler_info(args):
         tty.error("No compilers match spec %s" % cspec)
     else:
         for c in compilers:
-            print str(c.spec) + ":"
-            print "\tpaths:"
+            print(str(c.spec) + ":")
+            print("\tpaths:")
             for cpath in ['cc', 'cxx', 'f77', 'fc']:
-                print "\t\t%s = %s" % (cpath, getattr(c, cpath, None))
+                print("\t\t%s = %s" % (cpath, getattr(c, cpath, None)))
             if c.flags:
-                print "\tflags:"
-                for flag, flag_value in c.flags.iteritems():
-                    print "\t\t%s = %s" % (flag, flag_value)
+                print("\tflags:")
+                for flag, flag_value in iteritems(c.flags):
+                    print("\t\t%s = %s" % (flag, flag_value))
             if len(c.environment) != 0:
                 if len(c.environment['set']) != 0:
-                    print "\tenvironment:"
-                    print "\t    set:"
-                    for key, value in c.environment['set'].iteritems():
-                        print "\t        %s = %s" % (key, value)
+                    print("\tenvironment:")
+                    print("\t    set:")
+                    for key, value in iteritems(c.environment['set']):
+                        print("\t        %s = %s" % (key, value))
             if c.extra_rpaths:
-                print "\tExtra rpaths:"
+                print("\tExtra rpaths:")
                 for extra_rpath in c.extra_rpaths:
-                    print "\t\t%s" % extra_rpath
-            print "\tmodules  = %s" % c.modules
-            print "\toperating system  = %s" % c.operating_system
+                    print("\t\t%s" % extra_rpath)
+            print("\tmodules  = %s" % c.modules)
+            print("\toperating system  = %s" % c.operating_system)
 
 
 def compiler_list(args):
     tty.msg("Available compilers")
     index = index_by(spack.compilers.all_compilers(scope=args.scope),
                      lambda c: (c.spec.name, c.operating_system, c.target))
-    ordered_sections = sorted(index.items(), key=lambda (k, v): k)
+    ordered_sections = sorted(index.items(), key=lambda item: item[0])
     for i, (key, compilers) in enumerate(ordered_sections):
         if i >= 1:
-            print
+            print()
         name, os, target = key
         os_str = os
         if target:
diff --git a/lib/spack/spack/cmd/configure.py b/lib/spack/spack/cmd/configure.py
index b6669f33a2..037705f480 100644
--- a/lib/spack/spack/cmd/configure.py
+++ b/lib/spack/spack/cmd/configure.py
@@ -22,7 +22,6 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-
 import argparse
 
 import llnl.util.tty as tty
diff --git a/lib/spack/spack/cmd/dependents.py b/lib/spack/spack/cmd/dependents.py
index 42181b5502..c752ffb943 100644
--- a/lib/spack/spack/cmd/dependents.py
+++ b/lib/spack/spack/cmd/dependents.py
@@ -50,4 +50,4 @@ def dependents(parser, args):
     if deps:
         spack.cmd.display_specs(deps)
     else:
-        print "No dependents"
+        print("No dependents")
diff --git a/lib/spack/spack/cmd/env.py b/lib/spack/spack/cmd/env.py
index 49fc48700c..ed18940ac0 100644
--- a/lib/spack/spack/cmd/env.py
+++ b/lib/spack/spack/cmd/env.py
@@ -22,8 +22,11 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import os
 import argparse
+
 import llnl.util.tty as tty
 import spack.cmd
 import spack.build_environment as build_env
@@ -64,7 +67,7 @@ def env(parser, args):
     if not cmd:
         # If no command act like the "env" command and print out env vars.
         for key, val in os.environ.items():
-            print "%s=%s" % (key, val)
+            print("%s=%s" % (key, val))
 
     else:
         # Otherwise execute the command with the new environment
diff --git a/lib/spack/spack/cmd/flake8.py b/lib/spack/spack/cmd/flake8.py
index d5ed9adf18..47f531fe84 100644
--- a/lib/spack/spack/cmd/flake8.py
+++ b/lib/spack/spack/cmd/flake8.py
@@ -22,6 +22,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import re
 import os
 import sys
@@ -175,12 +177,12 @@ def flake8(parser, args):
                 file_list = changed_files()
             shutil.copy('.flake8', os.path.join(temp, '.flake8'))
 
-        print '======================================================='
-        print 'flake8: running flake8 code checks on spack.'
-        print
-        print 'Modified files:'
+        print('=======================================================')
+        print('flake8: running flake8 code checks on spack.')
+        print()
+        print('Modified files:')
         for filename in file_list:
-            print "  %s" % filename.strip()
+            print("  %s" % filename.strip())
         print('=======================================================')
 
         # filter files into a temporary directory with exemptions added.
@@ -196,7 +198,7 @@ def flake8(parser, args):
 
         if args.root_relative:
             # print results relative to repo root.
-            print output
+            print(output)
         else:
             # print results relative to current working directory
             def cwd_relative(path):
@@ -204,16 +206,16 @@ def flake8(parser, args):
                     os.path.join(spack.prefix, path.group(1)), os.getcwd())
 
             for line in output.split('\n'):
-                print re.sub(r'^(.*): \[', cwd_relative, line)
+                print(re.sub(r'^(.*): \[', cwd_relative, line))
 
         if flake8.returncode != 0:
-            print "Flake8 found errors."
+            print("Flake8 found errors.")
             sys.exit(1)
         else:
-            print "Flake8 checks were clean."
+            print("Flake8 checks were clean.")
 
     finally:
         if args.keep_temp:
-            print "temporary files are in ", temp
+            print("temporary files are in ", temp)
         else:
             shutil.rmtree(temp, ignore_errors=True)
diff --git a/lib/spack/spack/cmd/graph.py b/lib/spack/spack/cmd/graph.py
index 414b6d78ec..ee401d8fb7 100644
--- a/lib/spack/spack/cmd/graph.py
+++ b/lib/spack/spack/cmd/graph.py
@@ -22,8 +22,9 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-import argparse
+from __future__ import print_function
 
+import argparse
 import llnl.util.tty as tty
 
 import spack
@@ -96,5 +97,5 @@ def graph(parser, args):
     elif specs:  # ascii is default: user doesn't need to provide it explicitly
         graph_ascii(specs[0], debug=spack.debug, deptype=deptype)
         for spec in specs[1:]:
-            print  # extra line bt/w independent graphs
+            print()  # extra line bt/w independent graphs
             graph_ascii(spec, debug=spack.debug)
diff --git a/lib/spack/spack/cmd/info.py b/lib/spack/spack/cmd/info.py
index 1dd0ee4e78..799471ffcc 100644
--- a/lib/spack/spack/cmd/info.py
+++ b/lib/spack/spack/cmd/info.py
@@ -22,7 +22,10 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import textwrap
+
 from llnl.util.tty.colify import *
 import spack
 import spack.fetch_strategy as fs
@@ -50,12 +53,12 @@ def print_text_info(pkg):
     """Print out a plain text description of a package."""
     header = "{0}:   ".format(pkg.build_system_class)
 
-    print header, pkg.name
+    print(header, pkg.name)
     whitespaces = ''.join([' '] * (len(header) - len("Homepage: ")))
-    print "Homepage:", whitespaces, pkg.homepage
+    print("Homepage:", whitespaces, pkg.homepage)
 
-    print
-    print "Safe versions:  "
+    print()
+    print("Safe versions:  ")
 
     if not pkg.versions:
         print("    None")
@@ -63,20 +66,20 @@ def print_text_info(pkg):
         pad = padder(pkg.versions, 4)
         for v in reversed(sorted(pkg.versions)):
             f = fs.for_package_version(pkg, v)
-            print "    %s%s" % (pad(v), str(f))
+            print("    %s%s" % (pad(v), str(f)))
 
-    print
-    print "Variants:"
+    print()
+    print("Variants:")
     if not pkg.variants:
-        print "    None"
+        print("    None")
     else:
         pad = padder(pkg.variants, 4)
 
         maxv = max(len(v) for v in sorted(pkg.variants))
         fmt = "%%-%ss%%-10s%%s" % (maxv + 4)
 
-        print "    " + fmt % ('Name',   'Default',   'Description')
-        print
+        print("    " + fmt % ('Name',   'Default',   'Description'))
+        print()
         for name in sorted(pkg.variants):
             v = pkg.variants[name]
             default = 'on' if v.default else 'off'
@@ -85,26 +88,26 @@ def print_text_info(pkg):
             lines[1:] = ["      " + (" " * maxv) + l for l in lines[1:]]
             desc = "\n".join(lines)
 
-            print "    " + fmt % (name, default, desc)
+            print("    " + fmt % (name, default, desc))
 
-    print
-    print "Installation Phases:"
+    print()
+    print("Installation Phases:")
     phase_str = ''
     for phase in pkg.phases:
         phase_str += "    {0}".format(phase)
-    print phase_str
+    print(phase_str)
 
     for deptype in ('build', 'link', 'run'):
-        print
-        print "%s Dependencies:" % deptype.capitalize()
+        print()
+        print("%s Dependencies:" % deptype.capitalize())
         deps = sorted(pkg.dependencies_of_type(deptype))
         if deps:
             colify(deps, indent=4)
         else:
-            print "    None"
+            print("    None")
 
-    print
-    print "Virtual Packages: "
+    print()
+    print("Virtual Packages: ")
     if pkg.provided:
         inverse_map = {}
         for spec, whens in pkg.provided.items():
@@ -113,17 +116,17 @@ def print_text_info(pkg):
                     inverse_map[when] = set()
                 inverse_map[when].add(spec)
         for when, specs in reversed(sorted(inverse_map.items())):
-            print "    %s provides %s" % (
-                when, ', '.join(str(s) for s in specs))
+            print("    %s provides %s" % (
+                when, ', '.join(str(s) for s in specs)))
     else:
-        print "    None"
+        print("    None")
 
-    print
-    print "Description:"
+    print()
+    print("Description:")
     if pkg.__doc__:
-        print pkg.format_doc(indent=4)
+        print(pkg.format_doc(indent=4))
     else:
-        print "    None"
+        print("    None")
 
 
 def info(parser, args):
diff --git a/lib/spack/spack/cmd/list.py b/lib/spack/spack/cmd/list.py
index b5b699dccd..bcfb092945 100644
--- a/lib/spack/spack/cmd/list.py
+++ b/lib/spack/spack/cmd/list.py
@@ -22,12 +22,14 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import argparse
 import cgi
 import fnmatch
 import re
 import sys
-from StringIO import StringIO
+from six import StringIO
 
 import llnl.util.tty as tty
 import spack
@@ -123,42 +125,42 @@ def rst(pkgs):
     pkgs = [spack.repo.get(name) for name in pkg_names]
 
     print('.. _package-list:')
-    print('')
+    print()
     print('============')
     print('Package List')
     print('============')
-    print('')
+    print()
     print('This is a list of things you can install using Spack.  It is')
     print('automatically generated based on the packages in the latest Spack')
     print('release.')
-    print('')
+    print()
     print('Spack currently has %d mainline packages:' % len(pkgs))
-    print('')
+    print()
     print(rst_table('`%s`_' % p for p in pkg_names))
-    print('')
+    print()
 
     # Output some text for each package.
     for pkg in pkgs:
         print('-----')
-        print('')
+        print()
         print('.. _%s:' % pkg.name)
-        print('')
+        print()
         # Must be at least 2 long, breaks for single letter packages like R.
         print('-' * max(len(pkg.name), 2))
         print(pkg.name)
         print('-' * max(len(pkg.name), 2))
-        print('')
+        print()
         print('Homepage:')
         print('  * `%s <%s>`__' % (cgi.escape(pkg.homepage), pkg.homepage))
-        print('')
+        print()
         print('Spack package:')
         print('  * `%s/package.py <%s>`__' % (pkg.name, github_url(pkg)))
-        print('')
+        print()
         if pkg.versions:
             print('Versions:')
             print('  ' + ', '.join(str(v) for v in
                                    reversed(sorted(pkg.versions))))
-            print('')
+            print()
 
         for deptype in spack.alldeps:
             deps = pkg.dependencies_of_type(deptype)
@@ -166,11 +168,11 @@ def rst(pkgs):
                 print('%s Dependencies' % deptype.capitalize())
                 print('  ' + ', '.join('%s_' % d if d in pkg_names
                                        else d for d in deps))
-                print('')
+                print()
 
         print('Description:')
         print(pkg.format_doc(indent=2))
-        print('')
+        print()
 
 
 def list(parser, args):
diff --git a/lib/spack/spack/cmd/location.py b/lib/spack/spack/cmd/location.py
index c82b7072f9..d1a7825630 100644
--- a/lib/spack/spack/cmd/location.py
+++ b/lib/spack/spack/cmd/location.py
@@ -22,8 +22,9 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-import argparse
+from __future__ import print_function
 
+import argparse
 import llnl.util.tty as tty
 
 import spack
@@ -70,16 +71,16 @@ def setup_parser(subparser):
 
 def location(parser, args):
     if args.module_dir:
-        print spack.module_path
+        print(spack.module_path)
 
     elif args.spack_root:
-        print spack.prefix
+        print(spack.prefix)
 
     elif args.packages:
-        print spack.repo.first_repo().root
+        print(spack.repo.first_repo().root)
 
     elif args.stages:
-        print spack.stage_path
+        print(spack.stage_path)
 
     else:
         specs = spack.cmd.parse_specs(args.spec)
@@ -91,14 +92,14 @@ def location(parser, args):
         if args.install_dir:
             # install_dir command matches against installed specs.
             spec = spack.cmd.disambiguate_spec(specs[0])
-            print spec.prefix
+            print(spec.prefix)
 
         else:
             spec = specs[0]
 
             if args.package_dir:
                 # This one just needs the spec name.
-                print spack.repo.dirname_for_package_name(spec.name)
+                print(spack.repo.dirname_for_package_name(spec.name))
 
             else:
                 # These versions need concretized specs.
@@ -106,11 +107,11 @@ def location(parser, args):
                 pkg = spack.repo.get(spec)
 
                 if args.stage_dir:
-                    print pkg.stage.path
+                    print(pkg.stage.path)
 
                 else:  # args.build_dir is the default.
                     if not pkg.stage.source_path:
                         tty.die("Build directory does not exist yet. "
                                 "Run this to create it:",
                                 "spack stage " + " ".join(args.spec))
-                    print pkg.stage.source_path
+                    print(pkg.stage.source_path)
diff --git a/lib/spack/spack/cmd/md5.py b/lib/spack/spack/cmd/md5.py
index 7940d1327b..fc205cc693 100644
--- a/lib/spack/spack/cmd/md5.py
+++ b/lib/spack/spack/cmd/md5.py
@@ -25,7 +25,7 @@
 import argparse
 import hashlib
 import os
-from urlparse import urlparse
+from six.moves.urllib.parse import urlparse
 
 import llnl.util.tty as tty
 import spack.util.crypto
diff --git a/lib/spack/spack/cmd/mirror.py b/lib/spack/spack/cmd/mirror.py
index 2db75a0b1f..528fcbfc3f 100644
--- a/lib/spack/spack/cmd/mirror.py
+++ b/lib/spack/spack/cmd/mirror.py
@@ -141,7 +141,7 @@ def mirror_list(args):
     fmt = "%%-%ds%%s" % (max_len + 4)
 
     for name in mirrors:
-        print fmt % (name, mirrors[name])
+        print(fmt % (name, mirrors[name]))
 
 
 def _read_specs_from_file(filename):
@@ -152,7 +152,7 @@ def _read_specs_from_file(filename):
                 s = Spec(string)
                 s.package
                 specs.append(s)
-            except SpackError, e:
+            except SpackError as e:
                 tty.die("Parse error in %s, line %d:" % (args.file, i + 1),
                         ">>> " + string, str(e))
     return specs
diff --git a/lib/spack/spack/cmd/pkg.py b/lib/spack/spack/cmd/pkg.py
index 45104a9ff2..7b668586b5 100644
--- a/lib/spack/spack/cmd/pkg.py
+++ b/lib/spack/spack/cmd/pkg.py
@@ -22,6 +22,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import os
 
 import argparse
@@ -118,13 +120,13 @@ def pkg_diff(args):
     u1, u2 = diff_packages(args.rev1, args.rev2)
 
     if u1:
-        print "%s:" % args.rev1
+        print("%s:" % args.rev1)
         colify(sorted(u1), indent=4)
         if u1:
-            print
+            print()
 
     if u2:
-        print "%s:" % args.rev2
+        print("%s:" % args.rev2)
         colify(sorted(u2), indent=4)
 
 
diff --git a/lib/spack/spack/cmd/repo.py b/lib/spack/spack/cmd/repo.py
index 1881654cac..dd75f148c2 100644
--- a/lib/spack/spack/cmd/repo.py
+++ b/lib/spack/spack/cmd/repo.py
@@ -22,6 +22,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import os
 
 import llnl.util.tty as tty
@@ -161,7 +163,7 @@ def repo_list(args):
     max_ns_len = max(len(r.namespace) for r in repos)
     for repo in repos:
         fmt = "%%-%ds%%s" % (max_ns_len + 4)
-        print fmt % (repo.namespace, repo.root)
+        print(fmt % (repo.namespace, repo.root))
 
 
 def repo(parser, args):
diff --git a/lib/spack/spack/cmd/spec.py b/lib/spack/spack/cmd/spec.py
index 9eea404bc7..d89707f230 100644
--- a/lib/spack/spack/cmd/spec.py
+++ b/lib/spack/spack/cmd/spec.py
@@ -22,8 +22,9 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-import argparse
+from __future__ import print_function
 
+import argparse
 import spack
 import spack.cmd
 import spack.cmd.common.arguments as arguments
@@ -69,20 +70,20 @@ def spec(parser, args):
         # With -y, just print YAML to output.
         if args.yaml:
             spec.concretize()
-            print spec.to_yaml()
+            print(spec.to_yaml())
             continue
 
         # Print some diagnostic info by default.
-        print "Input spec"
-        print "--------------------------------"
-        print spec.tree(**kwargs)
+        print("Input spec")
+        print("--------------------------------")
+        print(spec.tree(**kwargs))
 
-        print "Normalized"
-        print "--------------------------------"
+        print("Normalized")
+        print("--------------------------------")
         spec.normalize()
-        print spec.tree(**kwargs)
+        print(spec.tree(**kwargs))
 
-        print "Concretized"
-        print "--------------------------------"
+        print("Concretized")
+        print("--------------------------------")
         spec.concretize()
-        print spec.tree(**kwargs)
+        print(spec.tree(**kwargs))
diff --git a/lib/spack/spack/cmd/test.py b/lib/spack/spack/cmd/test.py
index c569a1bc88..9384e3a9e6 100644
--- a/lib/spack/spack/cmd/test.py
+++ b/lib/spack/spack/cmd/test.py
@@ -22,12 +22,14 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import sys
 import os
 import re
 import argparse
 import pytest
-from StringIO import StringIO
+from six import StringIO
 
 from llnl.util.filesystem import *
 from llnl.util.tty.colify import colify
@@ -79,7 +81,7 @@ def do_list(args, unknown_args):
                 output_lines.append(
                     os.path.basename(name).replace('.py', ''))
         else:
-            print indent + name
+            print(indent + name)
 
     if args.list:
         colify(output_lines)
diff --git a/lib/spack/spack/cmd/versions.py b/lib/spack/spack/cmd/versions.py
index dacca2489b..f65ef14406 100644
--- a/lib/spack/spack/cmd/versions.py
+++ b/lib/spack/spack/cmd/versions.py
@@ -22,6 +22,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 from llnl.util.tty.colify import colify
 import llnl.util.tty as tty
 import spack
@@ -47,10 +49,10 @@ def versions(parser, args):
     tty.msg("Remote versions (not yet checksummed):")
     if not remote_versions:
         if not fetched_versions:
-            print "  Found no versions for %s" % pkg.name
+            print("  Found no versions for %s" % pkg.name)
             tty.debug("Check the list_url and list_depth attribute on the "
                       "package to help Spack find versions.")
         else:
-            print "  Found no unckecksummed versions for %s" % pkg.name
+            print("  Found no unckecksummed versions for %s" % pkg.name)
     else:
         colify(sorted(remote_versions, reverse=True), indent=2)
diff --git a/lib/spack/spack/compiler.py b/lib/spack/spack/compiler.py
index 9e9c7cbcb4..90af900d0d 100644
--- a/lib/spack/spack/compiler.py
+++ b/lib/spack/spack/compiler.py
@@ -265,11 +265,11 @@ class Compiler(object):
                 full_path, prefix, suffix = key
                 version = detect_version(full_path)
                 return (version, prefix, suffix, full_path)
-            except ProcessError, e:
+            except ProcessError as e:
                 tty.debug(
                     "Couldn't get version for compiler %s" % full_path, e)
                 return None
-            except Exception, e:
+            except Exception as e:
                 # Catching "Exception" here is fine because it just
                 # means something went wrong running a candidate executable.
                 tty.debug("Error while executing candidate compiler %s"
diff --git a/lib/spack/spack/compilers/__init__.py b/lib/spack/spack/compilers/__init__.py
index a16caa3a6c..585df23320 100644
--- a/lib/spack/spack/compilers/__init__.py
+++ b/lib/spack/spack/compilers/__init__.py
@@ -335,7 +335,7 @@ def get_compiler_duplicates(compiler_spec, arch_spec):
             scope_to_compilers[scope] = compilers
 
     cfg_file_to_duplicates = dict()
-    for scope, compilers in scope_to_compilers.iteritems():
+    for scope, compilers in scope_to_compilers.items():
         config_file = config_scopes[scope].get_section_filename('compilers')
         cfg_file_to_duplicates[config_file] = compilers
 
@@ -401,7 +401,7 @@ class CompilerDuplicateError(spack.error.SpackError):
         config_file_to_duplicates = get_compiler_duplicates(
             compiler_spec, arch_spec)
         duplicate_table = list(
-            (x, len(y)) for x, y in config_file_to_duplicates.iteritems())
+            (x, len(y)) for x, y in config_file_to_duplicates.items())
         descriptor = lambda num: 'time' if num == 1 else 'times'
         duplicate_msg = (
             lambda cfgfile, count: "{0}: {1} {2}".format(
diff --git a/lib/spack/spack/concretize.py b/lib/spack/spack/concretize.py
index 126db8b780..6ab796810b 100644
--- a/lib/spack/spack/concretize.py
+++ b/lib/spack/spack/concretize.py
@@ -34,6 +34,8 @@ TODO: make this customizable and allow users to configure
       concretization  policies.
 """
 from __future__ import print_function
+from six import iteritems
+
 import spack
 import spack.spec
 import spack.compilers
@@ -241,7 +243,7 @@ class DefaultConcretizer(object):
 
     def concretize_architecture(self, spec):
         """If the spec is empty provide the defaults of the platform. If the
-        architecture is not a basestring, then check if either the platform,
+        architecture is not a string type, then check if either the platform,
         target or operating system are concretized. If any of the fields are
         changed then return True. If everything is concretized (i.e the
         architecture attribute is a namedtuple of classes) then return False.
@@ -262,7 +264,7 @@ class DefaultConcretizer(object):
         while not spec.architecture.concrete and default_archs:
             arch = default_archs.pop(0)
 
-            replacement_fields = [k for k, v in arch.to_cmp_dict().iteritems()
+            replacement_fields = [k for k, v in iteritems(arch.to_cmp_dict())
                                   if v and not getattr(spec.architecture, k)]
             for field in replacement_fields:
                 setattr(spec.architecture, field, getattr(arch, field))
diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index 56c6421457..7c3d614aee 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -52,6 +52,8 @@ import copy
 import os
 import re
 import sys
+from six import string_types
+from six import iteritems
 
 import yaml
 import jsonschema
@@ -108,7 +110,7 @@ def extend_with_default(validator_class):
         "patternProperties"]
 
     def set_defaults(validator, properties, instance, schema):
-        for property, subschema in properties.iteritems():
+        for property, subschema in iteritems(properties):
             if "default" in subschema:
                 instance.setdefault(property, subschema["default"])
         for err in validate_properties(
@@ -116,10 +118,10 @@ def extend_with_default(validator_class):
             yield err
 
     def set_pp_defaults(validator, properties, instance, schema):
-        for property, subschema in properties.iteritems():
+        for property, subschema in iteritems(properties):
             if "default" in subschema:
                 if isinstance(instance, dict):
-                    for key, val in instance.iteritems():
+                    for key, val in iteritems(instance):
                         if re.match(property, key) and val is None:
                             instance[key] = subschema["default"]
 
@@ -306,8 +308,8 @@ def _mark_overrides(data):
 
     elif isinstance(data, dict):
         marked = {}
-        for key, val in data.iteritems():
-            if isinstance(key, basestring) and key.endswith(':'):
+        for key, val in iteritems(data):
+            if isinstance(key, string_types) and key.endswith(':'):
                 key = syaml.syaml_str(key[:-1])
                 key.override = True
             marked[key] = _mark_overrides(val)
@@ -348,7 +350,7 @@ def _merge_yaml(dest, source):
 
     # Source dict is merged into dest.
     elif they_are(dict):
-        for sk, sv in source.iteritems():
+        for sk, sv in iteritems(source):
             if override(sk) or sk not in dest:
                 # if sk ended with ::, or if it's new, completely override
                 dest[sk] = copy.copy(sv)
diff --git a/lib/spack/spack/database.py b/lib/spack/spack/database.py
index c81512d682..c63da4cf2e 100644
--- a/lib/spack/spack/database.py
+++ b/lib/spack/spack/database.py
@@ -41,6 +41,8 @@ filesystem.
 """
 import os
 import socket
+from six import string_types
+from six import iteritems
 
 from yaml.error import MarkedYAMLError, YAMLError
 
@@ -260,7 +262,7 @@ class Database(object):
             raise ValueError("Invalid database format: %s" % format)
 
         try:
-            if isinstance(stream, basestring):
+            if isinstance(stream, string_types):
                 with open(stream, 'r') as f:
                     fdata = load(f)
             else:
@@ -511,7 +513,7 @@ class Database(object):
                 new_spec, path, installed, ref_count=0, explicit=explicit)
 
             # Connect dependencies from the DB to the new copy.
-            for name, dep in spec.dependencies_dict(_tracked_deps).iteritems():
+            for name, dep in iteritems(spec.dependencies_dict(_tracked_deps)):
                 dkey = dep.spec.dag_hash()
                 new_spec._add_dependency(self._data[dkey].spec, dep.deptypes)
                 self._data[dkey].ref_count += 1
diff --git a/lib/spack/spack/directives.py b/lib/spack/spack/directives.py
index 58eabb9e3b..db280cb5fd 100644
--- a/lib/spack/spack/directives.py
+++ b/lib/spack/spack/directives.py
@@ -51,6 +51,7 @@ import functools
 import inspect
 import os.path
 import re
+from six import string_types
 
 import llnl.util.lang
 import spack
@@ -174,7 +175,7 @@ class DirectiveMetaMixin(type):
         """
         global __all__
 
-        if isinstance(dicts, basestring):
+        if isinstance(dicts, string_types):
             dicts = (dicts, )
         if not isinstance(dicts, collections.Sequence):
             message = "dicts arg must be list, tuple, or string. Found {0}"
diff --git a/lib/spack/spack/directory_layout.py b/lib/spack/spack/directory_layout.py
index 28e6584fb2..ff23ced6eb 100644
--- a/lib/spack/spack/directory_layout.py
+++ b/lib/spack/spack/directory_layout.py
@@ -23,7 +23,6 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 import os
-import exceptions
 import shutil
 import glob
 import tempfile
@@ -137,7 +136,7 @@ class DirectoryLayout(object):
         if os.path.exists(path):
             try:
                 shutil.rmtree(path)
-            except exceptions.OSError as e:
+            except OSError as e:
                 raise RemoveFailedError(spec, path, e)
 
         path = os.path.dirname(path)
diff --git a/lib/spack/spack/environment.py b/lib/spack/spack/environment.py
index 1333054518..76b8e132d4 100644
--- a/lib/spack/spack/environment.py
+++ b/lib/spack/spack/environment.py
@@ -291,7 +291,7 @@ class EnvironmentModifications(object):
         shell_options = '{shell_options}'.format(**info)
         source_file = '{source_command} {file} {concatenate_on_success}'
 
-        dump_cmd = "import os, json; print json.dumps(dict(os.environ))"
+        dump_cmd = "import os, json; print(json.dumps(dict(os.environ)))"
         dump_environment = 'python -c "%s"' % dump_cmd
 
         # Construct the command that will be executed
diff --git a/lib/spack/spack/error.py b/lib/spack/spack/error.py
index b6261a05f4..cd1ae5b25c 100644
--- a/lib/spack/spack/error.py
+++ b/lib/spack/spack/error.py
@@ -22,8 +22,11 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import os
 import sys
+
 import llnl.util.tty as tty
 import spack
 import inspect
diff --git a/lib/spack/spack/fetch_strategy.py b/lib/spack/spack/fetch_strategy.py
index d510db568f..0f97dda8b8 100644
--- a/lib/spack/spack/fetch_strategy.py
+++ b/lib/spack/spack/fetch_strategy.py
@@ -46,6 +46,9 @@ import re
 import shutil
 import copy
 from functools import wraps
+from six import string_types
+from six import with_metaclass
+
 import llnl.util.tty as tty
 from llnl.util.filesystem import *
 import spack
@@ -74,20 +77,19 @@ def _needs_stage(fun):
     return wrapper
 
 
-class FetchStrategy(object):
+class FSMeta(type):
+    """This metaclass registers all fetch strategies in a list."""
+    def __init__(cls, name, bases, dict):
+        type.__init__(cls, name, bases, dict)
+        if cls.enabled:
+            all_strategies.append(cls)
+
 
+class FetchStrategy(with_metaclass(FSMeta, object)):
     """Superclass of all fetch strategies."""
     enabled = False  # Non-abstract subclasses should be enabled.
     required_attributes = None  # Attributes required in version() args.
 
-    class __metaclass__(type):
-
-        """This metaclass registers all fetch strategies in a list."""
-
-        def __init__(cls, name, bases, dict):
-            type.__init__(cls, name, bases, dict)
-            if cls.enabled:
-                all_strategies.append(cls)
 
     def __init__(self):
         # The stage is initialized late, so that fetch strategies can be
@@ -319,7 +321,7 @@ class URLFetchStrategy(FetchStrategy):
         # top-level directory.  We ignore hidden files to accomodate
         # these "semi-exploding" tarballs.
         files = os.listdir(tarball_container)
-        non_hidden = filter(lambda f: not f.startswith('.'), files)
+        non_hidden = [f for f in files if not f.startswith('.')]
         if len(non_hidden) == 1:
             expanded_dir = os.path.join(tarball_container, non_hidden[0])
             if os.path.isdir(expanded_dir):
@@ -461,7 +463,7 @@ class VCSFetchStrategy(FetchStrategy):
 
         patterns = kwargs.get('exclude', None)
         if patterns is not None:
-            if isinstance(patterns, basestring):
+            if isinstance(patterns, string_types):
                 patterns = [patterns]
             for p in patterns:
                 tar.add_default_arg('--exclude=%s' % p)
diff --git a/lib/spack/spack/graph.py b/lib/spack/spack/graph.py
index 91230263f1..04e6cc7fca 100644
--- a/lib/spack/spack/graph.py
+++ b/lib/spack/spack/graph.py
@@ -63,6 +63,7 @@ can take a number of specs as input.
 """
 
 from heapq import *
+from six import iteritems
 
 from llnl.util.lang import *
 from llnl.util.tty.color import *
@@ -562,7 +563,7 @@ def graph_dot(specs, deptype=None, static=False, out=None):
                 continue
 
             # Add edges for each depends_on in the package.
-            for dep_name, dep in spec.package.dependencies.iteritems():
+            for dep_name, dep in iteritems(spec.package.dependencies):
                 deps.add((spec.name, dep_name))
 
             # If the package provides something, add an edge for that.
diff --git a/lib/spack/spack/hooks/case_consistency.py b/lib/spack/spack/hooks/case_consistency.py
index faf38f7ae3..e9208ee9ff 100644
--- a/lib/spack/spack/hooks/case_consistency.py
+++ b/lib/spack/spack/hooks/case_consistency.py
@@ -23,6 +23,7 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 from __future__ import absolute_import
+
 import os
 import re
 import platform
diff --git a/lib/spack/spack/hooks/module_file_generation.py b/lib/spack/spack/hooks/module_file_generation.py
index 445cea4e91..ff9617ff1c 100644
--- a/lib/spack/spack/hooks/module_file_generation.py
+++ b/lib/spack/spack/hooks/module_file_generation.py
@@ -23,15 +23,16 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 import spack.modules
+from six import iteritems
 
 
 def post_install(pkg):
-    for item, cls in spack.modules.module_types.iteritems():
+    for item, cls in iteritems(spack.modules.module_types):
         generator = cls(pkg.spec)
         generator.write()
 
 
 def post_uninstall(pkg):
-    for item, cls in spack.modules.module_types.iteritems():
+    for item, cls in iteritems(spack.modules.module_types):
         generator = cls(pkg.spec)
         generator.remove()
diff --git a/lib/spack/spack/modules.py b/lib/spack/spack/modules.py
index a6ffded935..8c702f1111 100644
--- a/lib/spack/spack/modules.py
+++ b/lib/spack/spack/modules.py
@@ -46,6 +46,8 @@ import os.path
 import re
 import string
 import textwrap
+from six import iteritems
+from six import with_metaclass
 
 import llnl.util.tty as tty
 from llnl.util.filesystem import join_path, mkdirp
@@ -213,7 +215,7 @@ def parse_config_options(module_generator):
             for x in arglist:
                 yield (x, )
         else:
-            for x in arglist.iteritems():
+            for x in iteritems(arglist):
                 yield x
 
     for method, arglist in environment_actions.items():
@@ -246,17 +248,17 @@ def format_env_var_name(name):
     return name.replace('-', '_').upper()
 
 
-class EnvModule(object):
-    name = 'env_module'
-    formats = {}
+class ModuleMeta(type):
+    """Metaclass registers modules in themodule_types dict."""
+    def __init__(cls, name, bases, dict):
+        type.__init__(cls, name, bases, dict)
+        if cls.name != 'env_module' and cls.name in _module_config['enable']:
+            module_types[cls.name] = cls
 
-    class __metaclass__(type):
 
-        def __init__(cls, name, bases, dict):
-            type.__init__(cls, name, bases, dict)
-            if cls.name != 'env_module' and cls.name in _module_config[
-                    'enable']:
-                module_types[cls.name] = cls
+class EnvModule(with_metaclass(ModuleMeta, object)):
+    name = 'env_module'
+    formats = {}
 
     def __init__(self, spec=None):
         self.spec = spec
diff --git a/lib/spack/spack/operating_systems/cnl.py b/lib/spack/spack/operating_systems/cnl.py
index 7acab1cbcb..b5c759bbcb 100644
--- a/lib/spack/spack/operating_systems/cnl.py
+++ b/lib/spack/spack/operating_systems/cnl.py
@@ -54,7 +54,7 @@ class Cnl(OperatingSystem):
 
         # ensure all the version calls we made are cached in the parent
         # process, as well.  This speeds up Spack a lot.
-        clist = reduce(lambda x, y: x + y, compiler_lists)
+        clist = [comp for cl in compiler_lists for comp in cl]
         return clist
 
     def find_compiler(self, cmp_cls, *paths):
diff --git a/lib/spack/spack/package.py b/lib/spack/spack/package.py
index 80d65bd739..6b71c0f1a9 100644
--- a/lib/spack/spack/package.py
+++ b/lib/spack/spack/package.py
@@ -42,6 +42,9 @@ import re
 import sys
 import textwrap
 import time
+from six import StringIO
+from six import string_types
+from six import with_metaclass
 
 import llnl.util.lock
 import llnl.util.tty as tty
@@ -56,7 +59,7 @@ import spack.mirror
 import spack.repository
 import spack.url
 import spack.util.web
-from StringIO import StringIO
+
 from llnl.util.filesystem import *
 from llnl.util.lang import *
 from llnl.util.link_tree import LinkTree
@@ -238,7 +241,7 @@ def on_package_attributes(**attr_dict):
     return _execute_under_condition
 
 
-class PackageBase(object):
+class PackageBase(with_metaclass(PackageMeta, object)):
     """This is the superclass for all spack packages.
 
     ***The Package class***
@@ -475,7 +478,6 @@ class PackageBase(object):
     Package creators override functions like install() (all of them do this),
     clean() (some of them do this), and others to provide custom behavior.
     """
-    __metaclass__ = PackageMeta
     #
     # These are default values for instance variables.
     #
@@ -1115,6 +1117,13 @@ class PackageBase(object):
         finally:
             self.prefix_lock.release_write()
 
+    @contextlib.contextmanager
+    def _stage_and_write_lock(self):
+        """Prefix lock nested in a stage."""
+        with self.stage:
+            with self._prefix_write_lock():
+                yield
+
     def do_install(self,
                    keep_prefix=False,
                    keep_stage=False,
@@ -1233,7 +1242,7 @@ class PackageBase(object):
 
             self.stage.keep = keep_stage
 
-            with contextlib.nested(self.stage, self._prefix_write_lock()):
+            with self._stage_and_write_lock():
                 # Run the pre-install hook in the child process after
                 # the directory is created.
                 spack.hooks.pre_install(self)
@@ -1265,9 +1274,10 @@ class PackageBase(object):
                         input_stream=input_stream
                     )
                     with redirection_context as log_redirection:
-                        for phase_name, phase in zip(self.phases, self._InstallPhase_phases):  # NOQA: ignore=E501
+                        for phase_name, phase in zip(
+                                self.phases, self._InstallPhase_phases):
                             tty.msg(
-                                'Executing phase : \'{0}\''.format(phase_name)  # NOQA: ignore=E501
+                                'Executing phase : \'{0}\''.format(phase_name)
                             )
                             # Redirect stdout and stderr to daemon pipe
                             with log_redirection:
@@ -1355,7 +1365,7 @@ class PackageBase(object):
         """This function checks whether install succeeded."""
 
         def check_paths(path_list, filetype, predicate):
-            if isinstance(path_list, basestring):
+            if isinstance(path_list, string_types):
                 path_list = [path_list]
 
             for path in path_list:
diff --git a/lib/spack/spack/package_prefs.py b/lib/spack/spack/package_prefs.py
index 63f90d9b50..3dc90a8eb9 100644
--- a/lib/spack/spack/package_prefs.py
+++ b/lib/spack/spack/package_prefs.py
@@ -22,6 +22,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from six import string_types
+from six import iteritems
 
 import spack
 import spack.error
@@ -180,7 +182,7 @@ class PreferredPackages(object):
             variants = self.preferred.get(pkg, {}).get('variants', '')
             if variants:
                 break
-        if not isinstance(variants, basestring):
+        if not isinstance(variants, string_types):
             variants = " ".join(variants)
         pkg = spack.repo.get(pkgname)
         spec = spack.spec.Spec("%s %s" % (pkgname, variants))
@@ -233,7 +235,7 @@ def spec_externals(spec):
     if (not pkg_paths) and (not pkg_modules):
         return []
 
-    for external_spec, path in pkg_paths.iteritems():
+    for external_spec, path in iteritems(pkg_paths):
         if not path:
             # skip entries without paths (avoid creating extra Specs)
             continue
@@ -242,7 +244,7 @@ def spec_externals(spec):
         if external_spec.satisfies(spec):
             external_specs.append(external_spec)
 
-    for external_spec, module in pkg_modules.iteritems():
+    for external_spec, module in iteritems(pkg_modules):
         if not module:
             continue
 
diff --git a/lib/spack/spack/package_test.py b/lib/spack/spack/package_test.py
index e366b5f0e5..54f424d45e 100644
--- a/lib/spack/spack/package_test.py
+++ b/lib/spack/spack/package_test.py
@@ -45,15 +45,15 @@ def compile_c_and_execute(source_file, include_flags, link_flags):
 def compare_output(current_output, blessed_output):
     """Compare blessed and current output of executables."""
     if not (current_output == blessed_output):
-        print "Produced output does not match expected output."
-        print "Expected output:"
-        print '-' * 80
-        print blessed_output
-        print '-' * 80
-        print "Produced output:"
-        print '-' * 80
-        print current_output
-        print '-' * 80
+        print("Produced output does not match expected output.")
+        print("Expected output:")
+        print('-' * 80)
+        print(blessed_output)
+        print('-' * 80)
+        print("Produced output:")
+        print('-' * 80)
+        print(current_output)
+        print('-' * 80)
         raise RuntimeError("Ouput check failed.",
                            "See spack_output.log for details")
 
diff --git a/lib/spack/spack/parse.py b/lib/spack/spack/parse.py
index e116175823..da11268bb2 100644
--- a/lib/spack/spack/parse.py
+++ b/lib/spack/spack/parse.py
@@ -25,6 +25,8 @@
 import re
 import shlex
 import itertools
+from six import string_types
+
 import spack.error
 
 
@@ -118,7 +120,7 @@ class Parser(object):
     def gettok(self):
         """Puts the next token in the input stream into self.next."""
         try:
-            self.next = self.tokens.next()
+            self.next = next(self.tokens)
         except StopIteration:
             self.next = None
 
@@ -159,7 +161,7 @@ class Parser(object):
             sys.exit(1)
 
     def setup(self, text):
-        if isinstance(text, basestring):
+        if isinstance(text, string_types):
             text = shlex.split(text)
         self.text = text
         self.push_tokens(self.lexer.lex(text))
diff --git a/lib/spack/spack/provider_index.py b/lib/spack/spack/provider_index.py
index 0e771c6255..7dee838619 100644
--- a/lib/spack/spack/provider_index.py
+++ b/lib/spack/spack/provider_index.py
@@ -26,6 +26,7 @@
 The ``virtual`` module contains utility classes for virtual dependencies.
 """
 from itertools import product as iproduct
+from six import iteritems
 from pprint import pformat
 
 import spack.util.spack_yaml as syaml
@@ -97,7 +98,7 @@ class ProviderIndex(object):
         assert(not spec.virtual)
 
         pkg = spec.package
-        for provided_spec, provider_specs in pkg.provided.iteritems():
+        for provided_spec, provider_specs in iteritems(pkg.provided):
             for provider_spec in provider_specs:
                 # TODO: fix this comment.
                 # We want satisfaction other than flags
@@ -201,7 +202,7 @@ class ProviderIndex(object):
     def from_yaml(stream):
         try:
             yfile = syaml.load(stream)
-        except MarkedYAMLError, e:
+        except MarkedYAMLError as e:
             raise spack.spec.SpackYAMLError(
                 "error parsing YAML ProviderIndex cache:", str(e))
 
@@ -288,7 +289,7 @@ def _transform(providers, transform_fun, out_mapping_type=dict):
     """
     def mapiter(mappings):
         if isinstance(mappings, dict):
-            return mappings.iteritems()
+            return iteritems(mappings)
         else:
             return iter(mappings)
 
diff --git a/lib/spack/spack/repository.py b/lib/spack/spack/repository.py
index 1536ecb0e6..5486f7a9a4 100644
--- a/lib/spack/spack/repository.py
+++ b/lib/spack/spack/repository.py
@@ -26,7 +26,6 @@ import os
 import stat
 import shutil
 import errno
-import exceptions
 import sys
 import inspect
 import imp
@@ -558,7 +557,7 @@ class Repo(object):
 
                 return yaml_data['repo']
 
-        except exceptions.IOError:
+        except IOError:
             tty.die("Error reading %s when opening %s"
                     % (self.config_file, self.root))
 
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 08b92cf705..8b0e560c8a 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -97,13 +97,14 @@ expansion when it is the first character in an id typed on the command line.
 """
 import base64
 import collections
-import csv
 import ctypes
 import hashlib
 import itertools
 from operator import attrgetter
+from six import StringIO
+from six import string_types
+from six import iteritems
 
-import cStringIO
 import llnl.util.tty as tty
 import spack
 import spack.architecture
@@ -113,7 +114,7 @@ import spack.parse
 import spack.store
 import spack.util.spack_json as sjson
 import spack.util.spack_yaml as syaml
-from cStringIO import StringIO
+
 from llnl.util.filesystem import find_libraries
 from llnl.util.lang import *
 from llnl.util.tty.color import *
@@ -222,7 +223,7 @@ def canonical_deptype(deptype):
     if deptype is None:
         return alldeps
 
-    elif isinstance(deptype, str):
+    elif isinstance(deptype, string_types):
         return special_types.get(deptype, (deptype,))
 
     elif isinstance(deptype, (tuple, list)):
@@ -270,7 +271,7 @@ class ArchSpec(object):
             spec_like = args[0]
             if isinstance(spec_like, ArchSpec):
                 self._dup(spec_like)
-            elif isinstance(spec_like, basestring):
+            elif isinstance(spec_like, string_types):
                 spec_fields = spec_like.split("-")
 
                 if len(spec_fields) == 3:
@@ -391,7 +392,7 @@ class ArchSpec(object):
             raise UnsatisfiableArchitectureSpecError(self, other)
 
         constrained = False
-        for attr, svalue in self.to_cmp_dict().iteritems():
+        for attr, svalue in iteritems(self.to_cmp_dict()):
             ovalue = getattr(other, attr)
             if svalue is None and ovalue is not None:
                 setattr(self, attr, ovalue)
@@ -406,7 +407,7 @@ class ArchSpec(object):
 
     @property
     def concrete(self):
-        return all(v for k, v in self.to_cmp_dict().iteritems())
+        return all(v for k, v in iteritems(self.to_cmp_dict()))
 
     def to_cmp_dict(self):
         """Returns a dictionary that can be used for field comparison."""
@@ -464,7 +465,7 @@ 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, basestring):
+            if isinstance(arg, string_types):
                 c = SpecParser().parse_compiler(arg)
                 self.name = c.name
                 self.versions = c.versions
@@ -728,7 +729,7 @@ class FlagMap(HashableMap):
         return clone
 
     def _cmp_key(self):
-        return tuple((k, tuple(v)) for k, v in sorted(self.iteritems()))
+        return tuple((k, tuple(v)) for k, v in sorted(iteritems(self)))
 
     def __str__(self):
         sorted_keys = filter(
@@ -918,7 +919,7 @@ class Spec(object):
             return
 
         # Parse if the spec_like is a string.
-        if not isinstance(spec_like, basestring):
+        if not isinstance(spec_like, string_types):
             raise TypeError("Can't make spec out of %s" % type(spec_like))
 
         spec_list = SpecParser().parse(spec_like)
@@ -1018,9 +1019,9 @@ class Spec(object):
         if name in self.variants:
             raise DuplicateVariantError(
                 "Cannot specify variant '%s' twice" % name)
-        if isinstance(value, basestring) and value.upper() == 'TRUE':
+        if isinstance(value, string_types) and value.upper() == 'TRUE':
             value = True
-        elif isinstance(value, basestring) and value.upper() == 'FALSE':
+        elif isinstance(value, string_types) and value.upper() == 'FALSE':
             value = False
         self.variants[name] = VariantSpec(name, value)
 
@@ -1056,7 +1057,7 @@ 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 kwargs.iteritems()
+            new_attrvals = [(a, v) for a, v in iteritems(kwargs)
                             if a in arch_attrs]
             for new_attr, new_value in new_attrvals:
                 if getattr(self.architecture, new_attr):
@@ -1219,7 +1220,7 @@ class Spec(object):
         # get initial values for kwargs
         depth = kwargs.get('depth', False)
         key_fun = kwargs.get('key', id)
-        if isinstance(key_fun, basestring):
+        if isinstance(key_fun, string_types):
             key_fun = attrgetter(key_fun)
         yield_root = kwargs.get('root', True)
         cover = kwargs.get('cover', 'nodes')
@@ -1314,7 +1315,7 @@ class Spec(object):
         else:
             yaml_text = syaml.dump(
                 self.to_node_dict(), default_flow_style=True, width=maxint)
-            sha = hashlib.sha1(yaml_text)
+            sha = hashlib.sha1(yaml_text.encode('utf-8'))
             b32_hash = base64.b32encode(sha.digest()).lower()
             if self.concrete:
                 self._hash = b32_hash
@@ -1421,7 +1422,7 @@ class Spec(object):
         formats so that reindex will work on old specs/databases.
         """
         for dep_name, elt in dependency_dict.items():
-            if isinstance(elt, basestring):
+            if isinstance(elt, string_types):
                 # original format, elt is just the dependency hash.
                 dag_hash, deptypes = elt, ['build', 'link']
             elif isinstance(elt, tuple):
@@ -2413,11 +2414,8 @@ class Spec(object):
         if query_parameters:
             # We have extra query parameters, which are comma separated
             # values
-            f = cStringIO.StringIO(query_parameters.pop())
-            try:
-                query_parameters = next(csv.reader(f, skipinitialspace=True))
-            except StopIteration:
-                query_parameters = ['']
+            csv = query_parameters.pop().strip()
+            query_parameters = re.split(r'\s*,\s*', csv)
 
         try:
             value = next(
diff --git a/lib/spack/spack/stage.py b/lib/spack/spack/stage.py
index 91f77839d8..03b7f5ef33 100644
--- a/lib/spack/spack/stage.py
+++ b/lib/spack/spack/stage.py
@@ -29,18 +29,19 @@ import hashlib
 import shutil
 import tempfile
 import getpass
-from urlparse import urljoin
+from six import string_types
+from six import iteritems
+from six.moves.urllib.parse import urljoin
 
 import llnl.util.tty as tty
 import llnl.util.lock
 from llnl.util.filesystem import *
 
-import spack.util.pattern as pattern
-
 import spack
 import spack.config
-import spack.fetch_strategy as fs
 import spack.error
+import spack.fetch_strategy as fs
+import spack.util.pattern as pattern
 from spack.version import *
 from spack.util.path import canonicalize_path
 from spack.util.crypto import prefix_bits, bit_length
@@ -84,7 +85,7 @@ def get_tmp_root():
     if _tmp_root is None:
         config = spack.config.get_config('config')
         candidates = config['build_stage']
-        if isinstance(candidates, basestring):
+        if isinstance(candidates, string_types):
             candidates = [candidates]
 
         path = _first_accessible_path(candidates)
@@ -188,7 +189,7 @@ 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, basestring):
+        if isinstance(url_or_fetch_strategy, string_types):
             self.fetcher = fs.from_url(url_or_fetch_strategy)
         elif isinstance(url_or_fetch_strategy, fs.FetchStrategy):
             self.fetcher = url_or_fetch_strategy
@@ -548,7 +549,7 @@ class ResourceStage(Stage):
         if not isinstance(placement, dict):
             placement = {'': placement}
         # Make the paths in the dictionary absolute and link
-        for key, value in placement.iteritems():
+        for key, value in iteritems(placement):
             target_path = join_path(
                 root_stage.source_path, resource.destination)
             destination_path = join_path(target_path, value)
@@ -661,7 +662,7 @@ class DIYStage(object):
 def _get_mirrors():
     """Get mirrors from spack configuration."""
     config = spack.config.get_config('mirrors')
-    return [val for name, val in config.iteritems()]
+    return [val for name, val in iteritems(config)]
 
 
 def ensure_access(file=spack.stage_path):
diff --git a/lib/spack/spack/test/cmd/install.py b/lib/spack/spack/test/cmd/install.py
index 304eb04a55..b57d39b441 100644
--- a/lib/spack/spack/test/cmd/install.py
+++ b/lib/spack/spack/test/cmd/install.py
@@ -22,19 +22,19 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-import StringIO
 import argparse
 import codecs
 import collections
 import contextlib
 import unittest
+from six import StringIO
 
 import llnl.util.filesystem
 import spack
 import spack.cmd
 import spack.cmd.install as install
 
-FILE_REGISTRY = collections.defaultdict(StringIO.StringIO)
+FILE_REGISTRY = collections.defaultdict(StringIO)
 
 
 # Monkey-patch open to write module files to a StringIO instance
@@ -44,7 +44,7 @@ def mock_open(filename, mode, *args):
         message = 'test.test_install : unexpected opening mode for mock_open'
         raise RuntimeError(message)
 
-    FILE_REGISTRY[filename] = StringIO.StringIO()
+    FILE_REGISTRY[filename] = StringIO()
 
     try:
         yield FILE_REGISTRY[filename]
diff --git a/lib/spack/spack/test/compilers.py b/lib/spack/spack/test/compilers.py
index d0fc506f40..bc21ec886e 100644
--- a/lib/spack/spack/test/compilers.py
+++ b/lib/spack/spack/test/compilers.py
@@ -23,6 +23,7 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 import pytest
+from six import iteritems
 
 import spack.spec
 import spack.compilers as compilers
@@ -30,7 +31,7 @@ import spack.compilers as compilers
 
 @pytest.mark.usefixtures('config')
 class TestCompilers(object):
-    
+
     def test_get_compiler_duplicates(self):
         # In this case there is only one instance of the specified compiler in
         # the test configuration (so it is not actually a duplicate), but the
@@ -38,11 +39,11 @@ class TestCompilers(object):
         cfg_file_to_duplicates = compilers.get_compiler_duplicates(
             'gcc@4.5.0', spack.spec.ArchSpec('cray-CNL-xeon'))
         assert len(cfg_file_to_duplicates) == 1
-        cfg_file, duplicates = cfg_file_to_duplicates.iteritems().next()
+        cfg_file, duplicates = next(iteritems(cfg_file_to_duplicates))
         assert len(duplicates) == 1
 
     def test_all_compilers(self):
         all_compilers = compilers.all_compilers()
-        filtered = list(x for x in all_compilers if str(x.spec) == 'clang@3.3')
-        filtered = list(x for x in filtered if x.operating_system == 'SuSE11')
+        filtered = [x for x in all_compilers if str(x.spec) == 'clang@3.3']
+        filtered = [x for x in filtered if x.operating_system == 'SuSE11']
         assert len(filtered) == 1
diff --git a/lib/spack/spack/test/conftest.py b/lib/spack/spack/test/conftest.py
index f344727674..2b7dc594ac 100644
--- a/lib/spack/spack/test/conftest.py
+++ b/lib/spack/spack/test/conftest.py
@@ -27,11 +27,12 @@ import copy
 import os
 import re
 import shutil
+from six import StringIO
 
-import cStringIO
 import llnl.util.filesystem
 import llnl.util.lang
 import ordereddict_backport
+
 import py
 import pytest
 import spack
@@ -56,11 +57,8 @@ def no_stdin_duplication(monkeypatch):
     """Duplicating stdin (or any other stream) returns an empty
     cStringIO object.
     """
-    monkeypatch.setattr(
-        llnl.util.lang,
-        'duplicate_stream',
-        lambda x: cStringIO.StringIO()
-    )
+    monkeypatch.setattr(llnl.util.lang, 'duplicate_stream',
+                        lambda x: StringIO())
 
 
 @pytest.fixture(autouse=True)
@@ -181,6 +179,7 @@ def config(configuration_dir):
     spack.config.clear_config_caches()
 
 
+
 @pytest.fixture(scope='module')
 def database(tmpdir_factory, builtin_mock, config):
     """Creates a mock database with some packages installed note that
@@ -312,7 +311,7 @@ def mock_archive():
             "\ttouch $prefix/dummy_file\n"
             "EOF\n"
         )
-    os.chmod(configure_path, 0755)
+    os.chmod(configure_path, 0o755)
     # Archive it
     current = tmpdir.chdir()
     archive_name = '{0}.tar.gz'.format(repo_name)
diff --git a/lib/spack/spack/test/graph.py b/lib/spack/spack/test/graph.py
index ce7b07ed86..46dd4f1bc6 100644
--- a/lib/spack/spack/test/graph.py
+++ b/lib/spack/spack/test/graph.py
@@ -22,7 +22,7 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-from StringIO import StringIO
+from six import StringIO
 
 from spack.spec import Spec
 from spack.graph import AsciiGraph, topological_sort, graph_dot
diff --git a/lib/spack/spack/test/lock.py b/lib/spack/spack/test/lock.py
index 4f62cd85e9..214797c1f6 100644
--- a/lib/spack/spack/test/lock.py
+++ b/lib/spack/spack/test/lock.py
@@ -283,7 +283,7 @@ class LockTest(unittest.TestCase):
         # ensure lock file exists the first time, so we open it read-only
         # to begin wtih.
         touch(self.lock_path)
-        os.chmod(self.lock_path, 0444)
+        os.chmod(self.lock_path, 0o444)
 
         lock = Lock(self.lock_path)
         self.assertTrue(lock._reads == 0)
diff --git a/lib/spack/spack/test/make_executable.py b/lib/spack/spack/test/make_executable.py
index 87a43a529a..1b3f384a8b 100644
--- a/lib/spack/spack/test/make_executable.py
+++ b/lib/spack/spack/test/make_executable.py
@@ -46,7 +46,7 @@ class MakeExecutableTest(unittest.TestCase):
         with open(make_exe, 'w') as f:
             f.write('#!/bin/sh\n')
             f.write('echo "$@"')
-        os.chmod(make_exe, 0700)
+        os.chmod(make_exe, 0o700)
 
         path_put_first('PATH', [self.tmpdir])
 
diff --git a/lib/spack/spack/test/modules.py b/lib/spack/spack/test/modules.py
index bb1b0006f8..0eb54cba2c 100644
--- a/lib/spack/spack/test/modules.py
+++ b/lib/spack/spack/test/modules.py
@@ -24,14 +24,14 @@
 ##############################################################################
 import collections
 import contextlib
+from six import StringIO
 
-import cStringIO
 import pytest
 import spack.modules
 import spack.spec
 
 # Our "filesystem" for the tests below
-FILE_REGISTRY = collections.defaultdict(cStringIO.StringIO)
+FILE_REGISTRY = collections.defaultdict(StringIO)
 # Spec strings that will be used throughout the tests
 mpich_spec_string = 'mpich@3.0.4'
 mpileaks_spec_string = 'mpileaks'
@@ -48,7 +48,7 @@ def stringio_open(monkeypatch):
         if not mode == 'w':
             raise RuntimeError('unexpected opening mode for stringio_open')
 
-        FILE_REGISTRY[filename] = cStringIO.StringIO()
+        FILE_REGISTRY[filename] = StringIO()
 
         try:
             yield FILE_REGISTRY[filename]
diff --git a/lib/spack/spack/test/multimethod.py b/lib/spack/spack/test/multimethod.py
index fbcc70afe8..003936a77a 100644
--- a/lib/spack/spack/test/multimethod.py
+++ b/lib/spack/spack/test/multimethod.py
@@ -86,7 +86,7 @@ def test_default_works(builtin_mock):
 
 def test_target_match(builtin_mock):
     platform = spack.architecture.platform()
-    targets = platform.targets.values()
+    targets = list(platform.targets.values())
     for target in targets[:-1]:
         pkg = spack.repo.get('multimethod target=' + target.name)
         assert pkg.different_by_target() == target.name
diff --git a/lib/spack/spack/test/pattern.py b/lib/spack/spack/test/pattern.py
index 0c772a0d2d..b76f88e670 100644
--- a/lib/spack/spack/test/pattern.py
+++ b/lib/spack/spack/test/pattern.py
@@ -86,6 +86,7 @@ class CompositeTest(unittest.TestCase):
         composite.append(self.Two())
         composite.add()
         self.assertEqual(self.Base.counter, 3)
+
         composite.pop()
         composite.subtract()
         self.assertEqual(self.Base.counter, 2)
diff --git a/lib/spack/spack/test/provider_index.py b/lib/spack/spack/test/provider_index.py
index a176d0c315..69a5c3cd40 100644
--- a/lib/spack/spack/test/provider_index.py
+++ b/lib/spack/spack/test/provider_index.py
@@ -37,7 +37,8 @@ Tests assume that mock packages provide this::
                     mpi@:10.0: set([zmpi])},
     'stuff': {stuff: set([externalvirtual])}}
 """
-import StringIO
+from six import StringIO
+
 import spack
 from spack.provider_index import ProviderIndex
 from spack.spec import Spec
@@ -46,10 +47,10 @@ from spack.spec import Spec
 def test_yaml_round_trip(builtin_mock):
     p = ProviderIndex(spack.repo.all_package_names())
 
-    ostream = StringIO.StringIO()
+    ostream = StringIO()
     p.to_yaml(ostream)
 
-    istream = StringIO.StringIO(ostream.getvalue())
+    istream = StringIO(ostream.getvalue())
     q = ProviderIndex.from_yaml(istream)
 
     assert p == q
diff --git a/lib/spack/spack/test/python_version.py b/lib/spack/spack/test/python_version.py
index 084eed7e33..ee0ff9d2c9 100644
--- a/lib/spack/spack/test/python_version.py
+++ b/lib/spack/spack/test/python_version.py
@@ -31,6 +31,8 @@ systems that ship with RHEL6/CentOS 6, which have Python 2.6 as the
 default version.  Once those go away, we can likely drop 2.6 and increase
 the minimum supported Python 3 version, as well.
 """
+from __future__ import print_function
+
 import os
 import sys
 import re
diff --git a/lib/spack/spack/test/spec_dag.py b/lib/spack/spack/test/spec_dag.py
index 2c414bd0c0..31d6203f7f 100644
--- a/lib/spack/spack/test/spec_dag.py
+++ b/lib/spack/spack/test/spec_dag.py
@@ -90,7 +90,7 @@ class TestSpecDag(object):
 
         names = ['mpileaks', 'callpath', 'dyninst', 'libdwarf', 'libelf',
                  'zmpi', 'fake']
-        pairs = zip([0, 1, 2, 3, 4, 2, 3], names)
+        pairs = list(zip([0, 1, 2, 3, 4, 2, 3], names))
 
         traversal = dag.traverse()
         assert [x.name for x in traversal] == names
@@ -104,7 +104,7 @@ class TestSpecDag(object):
 
         names = ['mpileaks', 'callpath', 'dyninst', 'libdwarf', 'libelf',
                  'libelf', 'zmpi', 'fake', 'zmpi']
-        pairs = zip([0, 1, 2, 3, 4, 3, 2, 3, 1], names)
+        pairs = list(zip([0, 1, 2, 3, 4, 3, 2, 3, 1], names))
 
         traversal = dag.traverse(cover='edges')
         assert [x.name for x in traversal] == names
@@ -118,7 +118,7 @@ class TestSpecDag(object):
 
         names = ['mpileaks', 'callpath', 'dyninst', 'libdwarf', 'libelf',
                  'libelf', 'zmpi', 'fake', 'zmpi', 'fake']
-        pairs = zip([0, 1, 2, 3, 4, 3, 2, 3, 1, 2], names)
+        pairs = list(zip([0, 1, 2, 3, 4, 3, 2, 3, 1, 2], names))
 
         traversal = dag.traverse(cover='paths')
         assert [x.name for x in traversal] == names
@@ -132,7 +132,7 @@ class TestSpecDag(object):
 
         names = ['libelf', 'libdwarf', 'dyninst', 'fake', 'zmpi',
                  'callpath', 'mpileaks']
-        pairs = zip([4, 3, 2, 3, 2, 1, 0], names)
+        pairs = list(zip([4, 3, 2, 3, 2, 1, 0], names))
 
         traversal = dag.traverse(order='post')
         assert [x.name for x in traversal] == names
@@ -146,7 +146,7 @@ class TestSpecDag(object):
 
         names = ['libelf', 'libdwarf', 'libelf', 'dyninst', 'fake', 'zmpi',
                  'callpath', 'zmpi', 'mpileaks']
-        pairs = zip([4, 3, 3, 2, 3, 2, 1, 1, 0], names)
+        pairs = list(zip([4, 3, 3, 2, 3, 2, 1, 1, 0], names))
 
         traversal = dag.traverse(cover='edges', order='post')
         assert [x.name for x in traversal] == names
@@ -160,7 +160,7 @@ class TestSpecDag(object):
 
         names = ['libelf', 'libdwarf', 'libelf', 'dyninst', 'fake', 'zmpi',
                  'callpath', 'fake', 'zmpi', 'mpileaks']
-        pairs = zip([4, 3, 3, 2, 3, 2, 1, 2, 1, 0], names)
+        pairs = list(zip([4, 3, 3, 2, 3, 2, 1, 2, 1, 0], names))
 
         traversal = dag.traverse(cover='paths', order='post')
         assert [x.name for x in traversal] == names
diff --git a/lib/spack/spack/url.py b/lib/spack/spack/url.py
index 89f4a16dfc..7502f23994 100644
--- a/lib/spack/spack/url.py
+++ b/lib/spack/spack/url.py
@@ -46,8 +46,8 @@ it's never been told about that version before.
 """
 import os
 import re
-from StringIO import StringIO
-from urlparse import urlsplit, urlunsplit
+from six import StringIO
+from six.moves.urllib.parse import urlsplit, urlunsplit
 
 import llnl.util.tty as tty
 from llnl.util.tty.color import *
@@ -486,7 +486,7 @@ def substitution_offsets(path):
     name_offsets = offsets[1::2]
 
     ver_offsets = []
-    for i in xrange(0, len(name_parts), 2):
+    for i in range(0, len(name_parts), 2):
         vparts = re.split(ver, name_parts[i])
         voffsets = cumsum(vparts, offsets[i], len)
         ver_offsets.extend(voffsets[1::2])
diff --git a/lib/spack/spack/util/executable.py b/lib/spack/spack/util/executable.py
index 7a960e88cb..372d0019e7 100644
--- a/lib/spack/spack/util/executable.py
+++ b/lib/spack/spack/util/executable.py
@@ -22,10 +22,10 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-
 import os
 import re
 import subprocess
+from six import string_types
 
 import llnl.util.tty as tty
 import spack
@@ -129,7 +129,7 @@ class Executable(object):
             raise ValueError("Cannot use `str` as input stream.")
 
         def streamify(arg, mode):
-            if isinstance(arg, basestring):
+            if isinstance(arg, string_types):
                 return open(arg, mode), True
             elif arg is str:
                 return subprocess.PIPE, False
diff --git a/lib/spack/spack/util/multiproc.py b/lib/spack/spack/util/multiproc.py
index 6a25c45713..91bac57c26 100644
--- a/lib/spack/spack/util/multiproc.py
+++ b/lib/spack/spack/util/multiproc.py
@@ -28,7 +28,6 @@ than multiprocessing.Pool.apply() can.  For example, apply() will fail
 to pickle functions if they're passed indirectly as parameters.
 """
 from multiprocessing import Process, Pipe, Semaphore, Value
-from itertools import izip
 
 __all__ = ['spawn', 'parmap', 'Barrier']
 
@@ -43,7 +42,7 @@ def spawn(f):
 def parmap(f, X):
     pipe = [Pipe() for x in X]
     proc = [Process(target=spawn(f), args=(c, x))
-            for x, (p, c) in izip(X, pipe)]
+            for x, (p, c) in zip(X, pipe)]
     [p.start() for p in proc]
     [p.join() for p in proc]
     return [p.recv() for (p, c) in pipe]
diff --git a/lib/spack/spack/util/naming.py b/lib/spack/spack/util/naming.py
index 9a5cdee411..1f2bfa88cf 100644
--- a/lib/spack/spack/util/naming.py
+++ b/lib/spack/spack/util/naming.py
@@ -27,7 +27,7 @@ from __future__ import absolute_import
 import string
 import itertools
 import re
-from StringIO import StringIO
+from six import StringIO
 
 import spack
 
diff --git a/lib/spack/spack/util/pattern.py b/lib/spack/spack/util/pattern.py
index b5731ccf08..7a1109f2d2 100644
--- a/lib/spack/spack/util/pattern.py
+++ b/lib/spack/spack/util/pattern.py
@@ -61,7 +61,7 @@ def composite(interface=None, method_list=None, container=list):
         # Retrieve the base class of the composite. Inspect its methods and
         # decide which ones will be overridden
         def no_special_no_private(x):
-            return inspect.ismethod(x) and not x.__name__.startswith('_')
+            return callable(x) and not x.__name__.startswith('_')
 
         # Patch the behavior of each of the methods in the previous list.
         # This is done associating an instance of the descriptor below to
@@ -90,42 +90,25 @@ def composite(interface=None, method_list=None, container=list):
                 return getter
 
         dictionary_for_type_call = {}
+
         # Construct a dictionary with the methods explicitly passed as name
         if method_list is not None:
-            # python@2.7: method_list_dict = {name: IterateOver(name) for name
-            # in method_list}
-            method_list_dict = {}
-            for name in method_list:
-                method_list_dict[name] = IterateOver(name)
-            dictionary_for_type_call.update(method_list_dict)
+            dictionary_for_type_call.update(
+                (name, IterateOver(name)) for name in method_list)
+
         # Construct a dictionary with the methods inspected from the interface
         if interface is not None:
-            ##########
-            # python@2.7: interface_methods = {name: method for name, method in
-            # inspect.getmembers(interface, predicate=no_special_no_private)}
-            interface_methods = {}
-            for name, method in inspect.getmembers(
-                    interface, predicate=no_special_no_private):
-                interface_methods[name] = method
-            ##########
-            # python@2.7: interface_methods_dict = {name: IterateOver(name,
-            # method) for name, method in interface_methods.iteritems()}
-            interface_methods_dict = {}
-            for name, method in interface_methods.iteritems():
-                interface_methods_dict[name] = IterateOver(name, method)
-            ##########
-            dictionary_for_type_call.update(interface_methods_dict)
+            dictionary_for_type_call.update(
+                (name, IterateOver(name, method))
+                for name, method in inspect.getmembers(
+                    interface, predicate=no_special_no_private))
+
         # Get the methods that are defined in the scope of the composite
         # class and override any previous definition
-        ##########
-        # python@2.7: cls_method = {name: method for name, method in
-        # inspect.getmembers(cls, predicate=inspect.ismethod)}
-        cls_method = {}
-        for name, method in inspect.getmembers(
-                cls, predicate=inspect.ismethod):
-            cls_method[name] = method
-        ##########
-        dictionary_for_type_call.update(cls_method)
+        dictionary_for_type_call.update(
+            (name, method) for name, method in inspect.getmembers(
+                cls, predicate=inspect.ismethod))
+
         # Generate the new class on the fly and return it
         # FIXME : inherit from interface if we start to use ABC classes?
         wrapper_class = type(cls.__name__, (cls, container),
diff --git a/lib/spack/spack/util/prefix.py b/lib/spack/spack/util/prefix.py
index 985d862269..bc6808f350 100644
--- a/lib/spack/spack/util/prefix.py
+++ b/lib/spack/spack/util/prefix.py
@@ -35,11 +35,11 @@ class Prefix(str):
        For example, you can do something like this::
 
            prefix = Prefix('/usr')
-           print prefix.lib
-           print prefix.lib64
-           print prefix.bin
-           print prefix.share
-           print prefix.man4
+           print(prefix.lib)
+           print(prefix.lib64)
+           print(prefix.bin)
+           print(prefix.share)
+           print(prefix.man4)
 
        This program would print:
 
@@ -52,7 +52,7 @@ class Prefix(str):
        Prefix objects behave identically to strings.  In fact, they
        subclass str.  So operators like + are legal:
 
-           print "foobar " + prefix
+           print("foobar " + prefix)
 
        This prints 'foobar /usr". All of this is meant to make custom
        installs easy.
diff --git a/lib/spack/spack/util/spack_json.py b/lib/spack/spack/util/spack_json.py
index 236eef8983..0090cf89ca 100644
--- a/lib/spack/spack/util/spack_json.py
+++ b/lib/spack/spack/util/spack_json.py
@@ -24,6 +24,9 @@
 ##############################################################################
 """Simple wrapper around JSON to guarantee consistent use of load/dump. """
 import json
+from six import string_types
+from six import iteritems
+
 import spack.error
 
 __all__ = ['load', 'dump', 'SpackJSONError']
@@ -36,7 +39,7 @@ _json_dump_args = {
 
 def load(stream):
     """Spack JSON needs to be ordered to support specs."""
-    if isinstance(stream, basestring):
+    if isinstance(stream, string_types):
         return _byteify(json.loads(stream, object_hook=_byteify),
                         ignore_dicts=True)
     else:
@@ -64,7 +67,7 @@ def _byteify(data, ignore_dicts=False):
     if isinstance(data, dict) and not ignore_dicts:
         return dict((_byteify(key, ignore_dicts=True),
                      _byteify(value, ignore_dicts=True)) for key, value in
-                    data.iteritems())
+                    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 9d4c607908..c49393af9c 100644
--- a/lib/spack/spack/util/spack_yaml.py
+++ b/lib/spack/spack/util/spack_yaml.py
@@ -137,7 +137,7 @@ class OrderedLineLoader(Loader):
             key = self.construct_object(key_node, deep=deep)
             try:
                 hash(key)
-            except TypeError, exc:
+            except TypeError as exc:
                 raise ConstructorError(
                     "while constructing a mapping", node.start_mark,
                     "found unacceptable key (%s)" % exc, key_node.start_mark)
diff --git a/lib/spack/spack/util/web.py b/lib/spack/spack/util/web.py
index 935532266f..8791f72753 100644
--- a/lib/spack/spack/util/web.py
+++ b/lib/spack/spack/util/web.py
@@ -25,10 +25,20 @@
 import re
 import os
 import sys
-import urllib2
-import urlparse
+
+from six.moves.urllib.request import urlopen, Request
+from six.moves.urllib.error import URLError
 from multiprocessing import Pool
-from HTMLParser import HTMLParser, HTMLParseError
+
+try:
+    # Python 2 had these in the HTMLParser package.
+    from HTMLParser import HTMLParser, HTMLParseError
+except ImportError:
+    # In Python 3, things moved to html.parser
+    from html.parser import HTMLParser
+    # Also, HTMLParseError is deprecated and never raised.
+    class HTMLParseError:
+        pass
 
 import llnl.util.tty as tty
 
@@ -80,9 +90,9 @@ def _spider(args):
         # It would be nice to do this with the HTTP Accept header to avoid
         # one round-trip.  However, most servers seem to ignore the header
         # if you ask for a tarball with Accept: text/html.
-        req = urllib2.Request(url)
+        req = Request(url)
         req.get_method = lambda: "HEAD"
-        resp = urllib2.urlopen(req, timeout=TIMEOUT)
+        resp = urlopen(req, timeout=TIMEOUT)
 
         if "Content-type" not in resp.headers:
             tty.debug("ignoring page " + url)
@@ -95,7 +105,7 @@ def _spider(args):
 
         # Do the real GET request when we know it's just HTML.
         req.get_method = lambda: "GET"
-        response = urllib2.urlopen(req, timeout=TIMEOUT)
+        response = urlopen(req, timeout=TIMEOUT)
         response_url = response.geturl()
 
         # Read the page and and stick it in the map we'll return
@@ -142,7 +152,7 @@ def _spider(args):
                 pool.terminate()
                 pool.join()
 
-    except urllib2.URLError as e:
+    except URLError as e:
         tty.debug(e)
         if raise_on_error:
             raise spack.error.NoNetworkConnectionError(str(e), url)
diff --git a/lib/spack/spack/version.py b/lib/spack/spack/version.py
index 0d68a709e8..739a8c4924 100644
--- a/lib/spack/spack/version.py
+++ b/lib/spack/spack/version.py
@@ -47,6 +47,7 @@ import re
 import numbers
 from bisect import bisect_left
 from functools import wraps
+from six import string_types
 
 from functools_backport import total_ordering
 from spack.util.spack_yaml import syaml_dict
@@ -216,7 +217,7 @@ class Version(object):
         segments = [a_or_n(seg) for seg in version]
 
         wc = segments[0]
-        for i in xrange(1, len(separators)):
+        for i in range(1, len(separators)):
             wc += '(?:' + separators[i] + segments[i]
 
         # Add possible alpha or beta indicator at the end of each segemnt
@@ -229,18 +230,24 @@ class Version(object):
 
     def __getitem__(self, idx):
         cls = type(self)
+
         if isinstance(idx, numbers.Integral):
             return self.version[idx]
+
         elif isinstance(idx, slice):
             # Currently len(self.separators) == len(self.version) - 1
             extendend_separators = self.separators + ('',)
             string_arg = []
-            for token, sep in zip(self.version, extendend_separators)[idx]:
+
+            pairs = zip(self.version[idx], extendend_separators[idx])
+            for token, sep in pairs:
                 string_arg.append(str(token))
                 string_arg.append(str(sep))
+
             string_arg.pop()  # We don't need the last separator
             string_arg = ''.join(string_arg)
             return cls(string_arg)
+
         message = '{cls.__name__} indices must be integers'
         raise TypeError(message.format(cls=cls))
 
@@ -375,9 +382,9 @@ class Version(object):
 class VersionRange(object):
 
     def __init__(self, start, end):
-        if isinstance(start, basestring):
+        if isinstance(start, string_types):
             start = Version(start)
-        if isinstance(end, basestring):
+        if isinstance(end, string_types):
             end = Version(end)
 
         self.start = start
@@ -568,7 +575,7 @@ class VersionList(object):
     def __init__(self, vlist=None):
         self.versions = []
         if vlist is not None:
-            if isinstance(vlist, basestring):
+            if isinstance(vlist, string_types):
                 vlist = _string_to_version(vlist)
                 if type(vlist) == VersionList:
                     self.versions = vlist.versions
@@ -796,7 +803,7 @@ def ver(obj):
     """
     if isinstance(obj, (list, tuple)):
         return VersionList(obj)
-    elif isinstance(obj, basestring):
+    elif isinstance(obj, string_types):
         return _string_to_version(obj)
     elif isinstance(obj, (int, float)):
         return _string_to_version(str(obj))