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brett.cannon
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Backport importlib in the form of providing importlib.import_module(). This has
been done purely to help transitions from 2.7 to 3.1. git-svn-id: http://svn.python.org/projects/python/trunk@68953 6015fed2-1504-0410-9fe1-9d1591cc4771
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‎Doc/library/importlib.rst‎

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:mod:`importlib` -- Convenience wrappers for :func:`__import__`
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===============================================================
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.. module:: importlib
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:synopsis: Convenience wrappers for __import__
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.. moduleauthor:: Brett Cannon <brett@python.org>
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.. sectionauthor:: Brett Cannon <brett@python.org>
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.. versionadded:: 2.7
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This module is a minor subset of what is available in the more full-featured
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package of the same name from Python 3.1 that provides a complete
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implementation of :keyword:`import`. What is here has been provided to
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help ease in transitioning from 2.7 to 3.1.
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.. function:: import_module(name, package=None)
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Import a module. The *name* argument specifies what module to
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import in absolute or relative terms
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(e.g. either ``pkg.mod`` or ``..mod``). If the name is
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specified in relative terms, then the *package* argument must be
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specified to the package which is to act as the anchor for resolving the
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package name (e.g. ``import_module('..mod', 'pkg.subpkg')`` will import
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``pkg.mod``). The specified module will be inserted into
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:data:`sys.modules` and returned.

‎Doc/library/modules.rst‎

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.. toctree::
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imp.rst
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importlib.rst
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imputil.rst
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zipimport.rst
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pkgutil.rst

‎Lib/importlib.py‎

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"""Backport of importlib.import_module from 3.x."""
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import sys
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def _resolve_name(name, package, level):
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"""Return the absolute name of the module to be imported."""
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level -= 1
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try:
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if package.count('.') < level:
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raise ValueError("attempted relative import beyond top-level "
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"package")
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except AttributeError:
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raise ValueError("__package__ not set to a string")
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base = package.rsplit('.', level)[0]
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if name:
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return "{0}.{1}".format(base, name)
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else:
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return base
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def import_module(name, package=None):
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"""Import a module.
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The 'package' argument is required when performing a relative import. It
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specifies the package to use as the anchor point from which to resolve the
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relative import to an absolute import.
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"""
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if name.startswith('.'):
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if not package:
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raise TypeError("relative imports require the 'package' argument")
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level = 0
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for character in name:
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if character != '.':
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break
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level += 1
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name = _resolve_name(name[level:], package, level)
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__import__(name)
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return sys.modules[name]

‎Lib/test/test_importlib.py‎

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import contextlib
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import imp
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import importlib
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import sys
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import unittest
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@contextlib.contextmanager
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def uncache(*names):
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"""Uncache a module from sys.modules.
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A basic sanity check is performed to prevent uncaching modules that either
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cannot/shouldn't be uncached.
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"""
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for name in names:
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if name in ('sys', 'marshal', 'imp'):
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raise ValueError(
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"cannot uncache {0} as it will break _importlib".format(name))
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try:
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del sys.modules[name]
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except KeyError:
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pass
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try:
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yield
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finally:
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for name in names:
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try:
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del sys.modules[name]
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except KeyError:
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pass
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@contextlib.contextmanager
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def import_state(**kwargs):
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"""Context manager to manage the various importers and stored state in the
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sys module.
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The 'modules' attribute is not supported as the interpreter state stores a
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pointer to the dict that the interpreter uses internally;
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reassigning to sys.modules does not have the desired effect.
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"""
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originals = {}
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try:
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for attr, default in (('meta_path', []), ('path', []),
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('path_hooks', []),
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('path_importer_cache', {})):
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originals[attr] = getattr(sys, attr)
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if attr in kwargs:
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new_value = kwargs[attr]
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del kwargs[attr]
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else:
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new_value = default
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setattr(sys, attr, new_value)
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if len(kwargs):
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raise ValueError(
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'unrecognized arguments: {0}'.format(kwargs.keys()))
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yield
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finally:
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for attr, value in originals.items():
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setattr(sys, attr, value)
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class mock_modules(object):
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"""A mock importer/loader."""
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def __init__(self, *names):
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self.modules = {}
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for name in names:
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if not name.endswith('.__init__'):
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import_name = name
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else:
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import_name = name[:-len('.__init__')]
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if '.' not in name:
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package = None
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elif import_name == name:
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package = name.rsplit('.', 1)[0]
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else:
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package = import_name
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module = imp.new_module(import_name)
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module.__loader__ = self
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module.__file__ = '<mock __file__>'
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module.__package__ = package
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module.attr = name
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if import_name != name:
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module.__path__ = ['<mock __path__>']
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self.modules[import_name] = module
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def __getitem__(self, name):
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return self.modules[name]
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def find_module(self, fullname, path=None):
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if fullname not in self.modules:
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return None
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else:
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return self
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def load_module(self, fullname):
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if fullname not in self.modules:
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raise ImportError
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else:
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sys.modules[fullname] = self.modules[fullname]
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return self.modules[fullname]
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def __enter__(self):
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self._uncache = uncache(*self.modules.keys())
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self._uncache.__enter__()
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return self
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def __exit__(self, *exc_info):
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self._uncache.__exit__(None, None, None)
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class ImportModuleTests(unittest.TestCase):
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"""Test importlib.import_module."""
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def test_module_import(self):
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# Test importing a top-level module.
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with mock_modules('top_level') as mock:
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with import_state(meta_path=[mock]):
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module = importlib.import_module('top_level')
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self.assertEqual(module.__name__, 'top_level')
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def test_absolute_package_import(self):
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# Test importing a module from a package with an absolute name.
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pkg_name = 'pkg'
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pkg_long_name = '{0}.__init__'.format(pkg_name)
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name = '{0}.mod'.format(pkg_name)
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with mock_modules(pkg_long_name, name) as mock:
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with import_state(meta_path=[mock]):
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module = importlib.import_module(name)
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self.assertEqual(module.__name__, name)
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def test_relative_package_import(self):
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# Test importing a module from a package through a relatve import.
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pkg_name = 'pkg'
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pkg_long_name = '{0}.__init__'.format(pkg_name)
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module_name = 'mod'
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absolute_name = '{0}.{1}'.format(pkg_name, module_name)
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relative_name = '.{0}'.format(module_name)
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with mock_modules(pkg_long_name, absolute_name) as mock:
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with import_state(meta_path=[mock]):
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module = importlib.import_module(relative_name, pkg_name)
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self.assertEqual(module.__name__, absolute_name)
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def test_absolute_import_with_package(self):
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# Test importing a module from a package with an absolute name with
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# the 'package' argument given.
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pkg_name = 'pkg'
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pkg_long_name = '{0}.__init__'.format(pkg_name)
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name = '{0}.mod'.format(pkg_name)
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with mock_modules(pkg_long_name, name) as mock:
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with import_state(meta_path=[mock]):
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module = importlib.import_module(name, pkg_name)
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self.assertEqual(module.__name__, name)
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def test_relative_import_wo_package(self):
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# Relative imports cannot happen without the 'package' argument being
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# set.
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self.assertRaises(TypeError, importlib.import_module, '.support')
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def test_main():
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from test.test_support import run_unittest
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run_unittest(ImportModuleTests)
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if __name__ == '__main__':
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test_main()

‎Misc/NEWS‎

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Library
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-------
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- Backport importlib from Python 3.1. Only the import_module() function has
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been backported to help facilitate transitions from 2.7 to 3.1.
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- Issue #1885: distutils. When running sdist with --formats=tar,gztar
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the tar file was overriden by the gztar one.
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