Viewing file:  test_caching.py (3.88 KB) -rw-r--r--
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"""Test that sys.modules is used properly by import."""
from .. import util
import sys
from types import MethodType
import unittest
import warnings
class UseCache:
"""When it comes to sys.modules, import prefers it over anything else.
Once a name has been resolved, sys.modules is checked to see if it contains
the module desired. If so, then it is returned [use cache]. If it is not
found, then the proper steps are taken to perform the import, but
sys.modules is still used to return the imported module (e.g., not what a
loader returns) [from cache on return]. This also applies to imports of
things contained within a package and thus get assigned as an attribute
[from cache to attribute] or pulled in thanks to a fromlist import
[from cache for fromlist]. But if sys.modules contains None then
ImportError is raised [None in cache].
"""
def test_using_cache(self):
# [use cache]
module_to_use = "some module found!"
with util.uncache('some_module'):
sys.modules['some_module'] = module_to_use
module = self.__import__('some_module')
self.assertEqual(id(module_to_use), id(module))
def test_None_in_cache(self):
#[None in cache]
name = 'using_None'
with util.uncache(name):
sys.modules[name] = None
with self.assertRaises(ImportError) as cm:
self.__import__(name)
self.assertEqual(cm.exception.name, name)
(Frozen_UseCache,
Source_UseCache
) = util.test_both(UseCache, __import__=util.__import__)
class ImportlibUseCache(UseCache, unittest.TestCase):
# Pertinent only to PEP 302; exec_module() doesn't return a module.
__import__ = util.__import__['Source']
def create_mock(self, *names, return_=None):
mock = util.mock_modules(*names)
original_load = mock.load_module
def load_module(self, fullname):
original_load(fullname)
return return_
mock.load_module = MethodType(load_module, mock)
return mock
# __import__ inconsistent between loaders and built-in import when it comes
# to when to use the module in sys.modules and when not to.
def test_using_cache_after_loader(self):
# [from cache on return]
with warnings.catch_warnings():
warnings.simplefilter("ignore", ImportWarning)
with self.create_mock('module') as mock:
with util.import_state(meta_path=[mock]):
module = self.__import__('module')
self.assertEqual(id(module), id(sys.modules['module']))
# See test_using_cache_after_loader() for reasoning.
def test_using_cache_for_assigning_to_attribute(self):
# [from cache to attribute]
with warnings.catch_warnings():
warnings.simplefilter("ignore", ImportWarning)
with self.create_mock('pkg.__init__', 'pkg.module') as importer:
with util.import_state(meta_path=[importer]):
module = self.__import__('pkg.module')
self.assertTrue(hasattr(module, 'module'))
self.assertEqual(id(module.module),
id(sys.modules['pkg.module']))
# See test_using_cache_after_loader() for reasoning.
def test_using_cache_for_fromlist(self):
# [from cache for fromlist]
with warnings.catch_warnings():
warnings.simplefilter("ignore", ImportWarning)
with self.create_mock('pkg.__init__', 'pkg.module') as importer:
with util.import_state(meta_path=[importer]):
module = self.__import__('pkg', fromlist=['module'])
self.assertTrue(hasattr(module, 'module'))
self.assertEqual(id(module.module),
id(sys.modules['pkg.module']))
if __name__ == '__main__':
unittest.main()
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