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+# -*- test-case-name: twisted.test.test_reflect -*-
+# Copyright (c) Twisted Matrix Laboratories.
+# See LICENSE for details.
+
+"""
+Standardized versions of various cool and/or strange things that you can do
+with Python's reflection capabilities.
+"""
+
+import sys
+
+from jsonschema.compat import PY3
+
+
+class _NoModuleFound(Exception):
+ """
+ No module was found because none exists.
+ """
+
+
+
+class InvalidName(ValueError):
+ """
+ The given name is not a dot-separated list of Python objects.
+ """
+
+
+
+class ModuleNotFound(InvalidName):
+ """
+ The module associated with the given name doesn't exist and it can't be
+ imported.
+ """
+
+
+
+class ObjectNotFound(InvalidName):
+ """
+ The object associated with the given name doesn't exist and it can't be
+ imported.
+ """
+
+
+
+if PY3:
+ def reraise(exception, traceback):
+ raise exception.with_traceback(traceback)
+else:
+ exec("""def reraise(exception, traceback):
+ raise exception.__class__, exception, traceback""")
+
+reraise.__doc__ = """
+Re-raise an exception, with an optional traceback, in a way that is compatible
+with both Python 2 and Python 3.
+
+Note that on Python 3, re-raised exceptions will be mutated, with their
+C{__traceback__} attribute being set.
+
+@param exception: The exception instance.
+@param traceback: The traceback to use, or C{None} indicating a new traceback.
+"""
+
+
+def _importAndCheckStack(importName):
+ """
+ Import the given name as a module, then walk the stack to determine whether
+ the failure was the module not existing, or some code in the module (for
+ example a dependent import) failing. This can be helpful to determine
+ whether any actual application code was run. For example, to distiguish
+ administrative error (entering the wrong module name), from programmer
+ error (writing buggy code in a module that fails to import).
+
+ @param importName: The name of the module to import.
+ @type importName: C{str}
+ @raise Exception: if something bad happens. This can be any type of
+ exception, since nobody knows what loading some arbitrary code might
+ do.
+ @raise _NoModuleFound: if no module was found.
+ """
+ try:
+ return __import__(importName)
+ except ImportError:
+ excType, excValue, excTraceback = sys.exc_info()
+ while excTraceback:
+ execName = excTraceback.tb_frame.f_globals["__name__"]
+ # in Python 2 execName is None when an ImportError is encountered,
+ # where in Python 3 execName is equal to the importName.
+ if execName is None or execName == importName:
+ reraise(excValue, excTraceback)
+ excTraceback = excTraceback.tb_next
+ raise _NoModuleFound()
+
+
+
+def namedAny(name):
+ """
+ Retrieve a Python object by its fully qualified name from the global Python
+ module namespace. The first part of the name, that describes a module,
+ will be discovered and imported. Each subsequent part of the name is
+ treated as the name of an attribute of the object specified by all of the
+ name which came before it. For example, the fully-qualified name of this
+ object is 'twisted.python.reflect.namedAny'.
+
+ @type name: L{str}
+ @param name: The name of the object to return.
+
+ @raise InvalidName: If the name is an empty string, starts or ends with
+ a '.', or is otherwise syntactically incorrect.
+
+ @raise ModuleNotFound: If the name is syntactically correct but the
+ module it specifies cannot be imported because it does not appear to
+ exist.
+
+ @raise ObjectNotFound: If the name is syntactically correct, includes at
+ least one '.', but the module it specifies cannot be imported because
+ it does not appear to exist.
+
+ @raise AttributeError: If an attribute of an object along the way cannot be
+ accessed, or a module along the way is not found.
+
+ @return: the Python object identified by 'name'.
+ """
+ if not name:
+ raise InvalidName('Empty module name')
+
+ names = name.split('.')
+
+ # if the name starts or ends with a '.' or contains '..', the __import__
+ # will raise an 'Empty module name' error. This will provide a better error
+ # message.
+ if '' in names:
+ raise InvalidName(
+ "name must be a string giving a '.'-separated list of Python "
+ "identifiers, not %r" % (name,))
+
+ topLevelPackage = None
+ moduleNames = names[:]
+ while not topLevelPackage:
+ if moduleNames:
+ trialname = '.'.join(moduleNames)
+ try:
+ topLevelPackage = _importAndCheckStack(trialname)
+ except _NoModuleFound:
+ moduleNames.pop()
+ else:
+ if len(names) == 1:
+ raise ModuleNotFound("No module named %r" % (name,))
+ else:
+ raise ObjectNotFound('%r does not name an object' % (name,))
+
+ obj = topLevelPackage
+ for n in names[1:]:
+ obj = getattr(obj, n)
+
+ return obj