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