Issue 5354: Change API for import_fresh_module() to better support test_warnings use case (also fixes some bugs in the original implementation)
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@ -351,15 +351,39 @@ The :mod:`test.test_support` module defines the following functions:
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.. versionadded:: 2.7
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.. function:: import_fresh_module(name, blocked_names=None, deprecated=False)
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.. function:: import_fresh_module(name, fresh=(), blocked=(), deprecated=False)
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This function imports and returns a fresh copy of the named Python module. The
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``sys.modules`` cache is bypassed temporarily, and the ability to import the
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modules named in *blocked_names* is suppressed for the duration of the import.
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This function imports and returns a fresh copy of the named Python module
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by removing the named module from ``sys.modules`` before doing the import.
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Note that unlike :func:`reload`, the original module is not affected by
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this operation.
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*fresh* is an iterable of additional module names that are also removed
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from the ``sys.modules`` cache before doing the import.
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*blocked* is an iterable of module names that are replaced with :const:`0`
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in the module cache during the import to ensure that attempts to import
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them raise :exc:`ImportError`.
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The named module and any modules named in the *fresh* and *blocked*
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parameters are saved before starting the import and then reinserted into
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``sys.modules`` when the fresh import is complete.
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Module and package deprecation messages are suppressed during this import
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if *deprecated* is :const:`True`.
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This function will raise :exc:`unittest.SkipTest` is the named module
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cannot be imported.
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Example use::
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# Get copies of the warnings module for testing without
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# affecting the version being used by the rest of the test suite
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# One copy uses the C implementation, the other is forced to use
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# the pure Python fallback implementation
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py_warnings = import_fresh_module('warnings', blocked=['_warnings'])
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c_warnings = import_fresh_module('warnings', fresh=['_warnings'])
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.. versionadded:: 2.7
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@ -8,7 +8,7 @@ import sys
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# We do a bit of trickery here to be able to test both the C implementation
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# and the Python implementation of the module.
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import heapq as c_heapq
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py_heapq = test_support.import_fresh_module('heapq', ['_heapq'])
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py_heapq = test_support.import_fresh_module('heapq', blocked=['_heapq'])
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class TestHeap(unittest.TestCase):
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module = None
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@ -70,12 +70,43 @@ def import_module(name, deprecated=False):
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raise unittest.SkipTest(str(msg))
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def import_fresh_module(name, blocked_names=None, deprecated=False):
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def _save_and_remove_module(name, orig_modules):
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"""Helper function to save and remove a module from sys.modules
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Return value is True if the module was in sys.modules and
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False otherwise."""
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saved = True
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try:
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orig_modules[name] = sys.modules[name]
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except KeyError:
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saved = False
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else:
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del sys.modules[name]
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return saved
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def _save_and_block_module(name, orig_modules):
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"""Helper function to save and block a module in sys.modules
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Return value is True if the module was in sys.modules and
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False otherwise."""
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saved = True
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try:
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orig_modules[name] = sys.modules[name]
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except KeyError:
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saved = False
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sys.modules[name] = 0
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return saved
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def import_fresh_module(name, fresh=(), blocked=(), deprecated=False):
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"""Imports and returns a module, deliberately bypassing the sys.modules cache
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and importing a fresh copy of the module. Once the import is complete,
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the sys.modules cache is restored to its original state.
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Importing of modules named in blocked_names is prevented while the fresh import
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Modules named in fresh are also imported anew if needed by the import.
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Importing of modules named in blocked is prevented while the fresh import
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takes place.
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If deprecated is True, any module or package deprecation messages
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@ -83,21 +114,24 @@ def import_fresh_module(name, blocked_names=None, deprecated=False):
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# NOTE: test_heapq and test_warnings include extra sanity checks to make
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# sure that this utility function is working as expected
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with _ignore_deprecated_imports(deprecated):
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if blocked_names is None:
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blocked_names = ()
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# Keep track of modules saved for later restoration as well
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# as those which just need a blocking entry removed
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orig_modules = {}
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if name in sys.modules:
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orig_modules[name] = sys.modules[name]
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del sys.modules[name]
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names_to_remove = []
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_save_and_remove_module(name, orig_modules)
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try:
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for blocked in blocked_names:
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orig_modules[blocked] = sys.modules[blocked]
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sys.modules[blocked] = 0
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py_module = importlib.import_module(name)
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for fresh_name in fresh:
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_save_and_remove_module(fresh_name, orig_modules)
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for blocked_name in blocked:
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if not _save_and_block_module(blocked_name, orig_modules):
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names_to_remove.append(blocked_name)
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fresh_module = importlib.import_module(name)
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finally:
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for blocked, module in orig_modules.items():
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sys.modules[blocked] = module
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return py_module
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for orig_name, module in orig_modules.items():
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sys.modules[orig_name] = module
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for name_to_remove in names_to_remove:
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del sys.modules[name_to_remove]
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return fresh_module
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def get_attribute(obj, name):
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@ -10,8 +10,8 @@ import warning_tests
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import warnings as original_warnings
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py_warnings = test_support.import_fresh_module('warnings', ['_warnings'])
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c_warnings = test_support.import_fresh_module('warnings')
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py_warnings = test_support.import_fresh_module('warnings', blocked=['_warnings'])
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c_warnings = test_support.import_fresh_module('warnings', fresh=['_warnings'])
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@contextmanager
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def warnings_state(module):
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@ -839,6 +839,12 @@ Extension Modules
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Tests
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-----
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- Issue #5354: New test support function import_fresh_module() makes
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it easy to import both normal and optimised versions of modules.
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test_heapq and test_warnings have been adjusted to use it, tests for
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other modules with both C and Python implementations in the stdlib
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can be adjusted to use it over time.
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- Fix test_warnings to no longer reset the warnings filter.
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- Fix test_logging to no longer reset the warnings filter.
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