Added additional possibility to configure Patcher

- added argument that allows adding modules for patching that import file system modules under another name
- fixes pytest-dev#231

CHANGES.md

@@ -4,6 +4,8 @@ The release versions are PyPi releases.
 ## Version 3.3 (as yet unreleased)
 
 #### New Features
+  * Added possibility to patch modules that import file system modules under another name, 
+  e.g. `import os as '_os` ([#231](../../issues/231)).
   * Added support for `dir_fd` argument in several `os` functions ([#206](../../issues/206)). 
   * Added support for open file descriptor as path argument
     in `os.utime`, `os.chmod`, `os.chdir`, `os.chown`, `os.listdir`, `os.stat` and `os.lstat` 

fake_filesystem_unittest_test.py

@@ -26,6 +26,8 @@
 import tempfile
 import sys
 
+from import_as_example import check_if_exists
+
 if sys.version_info >= (3, 4):
     import pathlib
 
@@ -139,6 +141,22 @@ def test_fakepathlib(self):
             self.assertTrue(self.fs.Exists('/fake_file.txt'))
 
 
+class TestImportAsOtherName(fake_filesystem_unittest.TestCase):
+    def __init__(self, methodName='RunTest'):
+        special_names = {'import_as_example': {'os': '_os'}}
+        super(TestImportAsOtherName, self).__init__(methodName,
+                                                    special_names=special_names)
+
+    def setUp(self):
+        self.setUpPyfakefs()
+
+    def testFileExists(self):
+        file_path = '/foo/bar/baz'
+        self.fs.CreateFile(file_path)
+        self.assertTrue(self.fs.Exists(file_path))
+        self.assertTrue(check_if_exists(file_path))
+
+
 sys.path.append(os.path.join(os.path.dirname(__file__), 'fixtures'))
 import module_with_attributes
 
@@ -161,6 +179,8 @@ def testAttributes(self):
 
 
 import math as path
+
+
 class TestPatchPathUnittestFailing(TestPyfakefsUnittestBase):
     """Tests the default behavior regarding the argument patch_path:
        An own path module (in this case an alias to math) cannot be imported,

import_as_example.py

@@ -0,0 +1,21 @@
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Example module that is used for testing modules that import file system modules
+to be patched under another name.
+"""
+import os as _os
+
+
+def check_if_exists(filepath):
+    return _os.path.exists(filepath)

pyfakefs/fake_filesystem_unittest.py

@@ -63,7 +63,8 @@
 
 
 def load_doctests(loader, tests, ignore, module,
-                  additional_skip_names=None, patch_path=True):  # pylint: disable=unused-argument
+                  additional_skip_names=None,
+                  patch_path=True, special_names=None):  # pylint: disable=unused-argument
     """Load the doctest tests for the specified module into unittest.
         Args:
             loader, tests, ignore : arguments passed in from `load_tests()`
@@ -74,7 +75,7 @@ def load_doctests(loader, tests, ignore, module,
     File `example_test.py` in the pyfakefs release provides a usage example.
     """
     _patcher = Patcher(additional_skip_names=additional_skip_names,
-                       patch_path=patch_path)
+                       patch_path=patch_path, special_names=special_names)
     globs = _patcher.replaceGlobs(vars(module))
     tests.addTests(doctest.DocTestSuite(module,
                                         globs=globs,
@@ -88,7 +89,8 @@ class TestCase(unittest.TestCase):
     modules by fake implementations.
     """
 
-    def __init__(self, methodName='runTest', additional_skip_names=None, patch_path=True):
+    def __init__(self, methodName='runTest', additional_skip_names=None,
+                 patch_path=True, special_names=None):
         """Creates the test class instance and the stubber used to stub out
         file system related modules.
 
@@ -103,21 +105,34 @@ def __init__(self, methodName='runTest', additional_skip_names=None, patch_path=
                         from my_module import path
                 Irrespective of patch_path, module 'os.path' is still correctly faked
                 if imported the usual way using `import os` or `import os.path`.
+            special_names: A dictionary with module names as key and a dictionary as
+                value, where the key is the original name of the module to be patched,
+                and the value is the name as it is imported.
+                This allows to patch modules where some of the file system modules are
+                imported as another name (e.g. `import os as _os`).
 
         If you specify arguments `additional_skip_names` or `patch_path` here
         and you have DocTests, consider also specifying the same arguments to
         :py:func:`load_doctests`.
         
-        Example usage in a derived test class::
+        Example usage in derived test classes::
 
-          class MyTestCase(fake_filesystem_unittest.TestCase):
-            def __init__(self, methodName='runTest'):
-              super(MyTestCase, self).__init__(
-                    methodName=methodName, additional_skip_names=['posixpath'])
+            class MyTestCase(fake_filesystem_unittest.TestCase):
+                def __init__(self, methodName='runTest'):
+                    super(MyTestCase, self).__init__(
+                        methodName=methodName, additional_skip_names=['posixpath'])
+
+
+            class AnotherTestCase(fake_filesystem_unittest.TestCase):
+                def __init__(self, methodName='runTest'):
+                    # allow patching a module that imports `os` as `my_os`
+                    special_names = {'amodule': {'os': 'my_os'}}
+                    super(MyTestCase, self).__init__(
+                        methodName=methodName, special_names=special_names)
         """
         super(TestCase, self).__init__(methodName)
         self._stubber = Patcher(additional_skip_names=additional_skip_names,
-                                patch_path=patch_path)
+                                patch_path=patch_path, special_names=special_names)
 
     @property
     def fs(self):
@@ -210,10 +225,11 @@ class Patcher(object):
     if HAS_PATHLIB:
         SKIPNAMES.add('pathlib')
 
-    def __init__(self, additional_skip_names=None, patch_path=True):
+    def __init__(self, additional_skip_names=None, patch_path=True, special_names=None):
         """For a description of the arguments, see TestCase.__init__"""
 
         self._skipNames = self.SKIPNAMES.copy()
+        self._special_names = special_names or {}
         if additional_skip_names is not None:
             self._skipNames.update(additional_skip_names)
         self._patchPath = patch_path
@@ -282,17 +298,27 @@ def _findModules(self):
             # and a test in fake_filesystem_unittest_test.py, class
             # TestAttributesWithFakeModuleNames.
             if inspect.ismodule(module.__dict__.get('os')):
-                self._os_modules.add(module)
+                self._os_modules.add((module, 'os'))
             if self._patchPath and inspect.ismodule(module.__dict__.get('path')):
-                self._path_modules.add(module)
+                self._path_modules.add((module, 'path'))
             if self.HAS_PATHLIB and inspect.ismodule(module.__dict__.get('pathlib')):
-                self._pathlib_modules.add(module)
+                self._pathlib_modules.add((module, 'pathlib'))
             if inspect.ismodule(module.__dict__.get('shutil')):
-                self._shutil_modules.add(module)
+                self._shutil_modules.add((module, 'shutil'))
             if inspect.ismodule(module.__dict__.get('tempfile')):
-                self._tempfile_modules.add(module)
+                self._tempfile_modules.add((module, 'tempfile'))
             if inspect.ismodule(module.__dict__.get('io')):
-                self._io_modules.add(module)
+                self._io_modules.add((module, 'io'))
+            if module.__name__ in self._special_names:
+                module_names = self._special_names[module.__name__]
+                if 'os' in module_names:
+                    self._os_modules.add((module, module_names['os']))
+                if self._patchPath and 'path' in module_names:
+                    self._path_modules.add((module, module_names['path']))
+                if self.HAS_PATHLIB and 'pathlib' in module_names:
+                    self._pathlib_modules.add((module, module_names['pathlib']))
+                if 'io' in module_names:
+                    self._io_modules.add((module, module_names['io']))
 
     def _refresh(self):
         """Renew the fake file system and set the _isStale flag to `False`."""
@@ -326,19 +352,19 @@ def setUp(self, doctester=None):
             self._stubs.SmartSet(builtins, 'file', self.fake_open)
         self._stubs.SmartSet(builtins, 'open', self.fake_open)
 
-        for module in self._os_modules:
-            self._stubs.SmartSet(module, 'os', self.fake_os)
-        for module in self._path_modules:
-            self._stubs.SmartSet(module, 'path', self.fake_path)
+        for module, attr in self._os_modules:
+            self._stubs.SmartSet(module, attr, self.fake_os)
+        for module, attr in self._path_modules:
+            self._stubs.SmartSet(module, attr, self.fake_path)
         if self.HAS_PATHLIB:
-            for module in self._pathlib_modules:
-                self._stubs.SmartSet(module, 'pathlib', self.fake_pathlib)
-        for module in self._shutil_modules:
-            self._stubs.SmartSet(module, 'shutil', self.fake_shutil)
-        for module in self._tempfile_modules:
-            self._stubs.SmartSet(module, 'tempfile', self.fake_tempfile_)
-        for module in self._io_modules:
-            self._stubs.SmartSet(module, 'io', self.fake_io)
+            for module, attr in self._pathlib_modules:
+                self._stubs.SmartSet(module, attr, self.fake_pathlib)
+        for module, attr in self._shutil_modules:
+            self._stubs.SmartSet(module, attr, self.fake_shutil)
+        for module, attr in self._tempfile_modules:
+            self._stubs.SmartSet(module, attr, self.fake_tempfile_)
+        for module, attr in self._io_modules:
+            self._stubs.SmartSet(module, attr, self.fake_io)
 
     def replaceGlobs(self, globs_):
         globs = globs_.copy()