143 lines
4.9 KiB
Python
143 lines
4.9 KiB
Python
#!/usr/bin/python2.4
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#
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# Copyright 2008 Google Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import inspect
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class StubOutForTesting:
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"""Sample Usage:
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You want os.path.exists() to always return true during testing.
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stubs = StubOutForTesting()
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stubs.Set(os.path, 'exists', lambda x: 1)
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...
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stubs.UnsetAll()
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The above changes os.path.exists into a lambda that returns 1. Once
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the ... part of the code finishes, the UnsetAll() looks up the old value
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of os.path.exists and restores it.
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"""
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def __init__(self):
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self.cache = []
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self.stubs = []
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def __del__(self):
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self.SmartUnsetAll()
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self.UnsetAll()
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def SmartSet(self, obj, attr_name, new_attr):
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"""Replace obj.attr_name with new_attr. This method is smart and works
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at the module, class, and instance level while preserving proper
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inheritance. It will not stub out C types however unless that has been
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explicitly allowed by the type.
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This method supports the case where attr_name is a staticmethod or a
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classmethod of obj.
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Notes:
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- If obj is an instance, then it is its class that will actually be
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stubbed. Note that the method Set() does not do that: if obj is
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an instance, it (and not its class) will be stubbed.
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- The stubbing is using the builtin getattr and setattr. So, the __get__
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and __set__ will be called when stubbing (TODO: A better idea would
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probably be to manipulate obj.__dict__ instead of getattr() and
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setattr()).
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Raises AttributeError if the attribute cannot be found.
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"""
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if (inspect.ismodule(obj) or
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(not inspect.isclass(obj) and obj.__dict__.has_key(attr_name))):
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orig_obj = obj
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orig_attr = getattr(obj, attr_name)
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else:
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if not inspect.isclass(obj):
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mro = list(inspect.getmro(obj.__class__))
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else:
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mro = list(inspect.getmro(obj))
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mro.reverse()
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orig_attr = None
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for cls in mro:
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try:
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orig_obj = cls
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orig_attr = getattr(obj, attr_name)
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except AttributeError:
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continue
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if orig_attr is None:
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raise AttributeError("Attribute not found.")
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# Calling getattr() on a staticmethod transforms it to a 'normal' function.
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# We need to ensure that we put it back as a staticmethod.
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old_attribute = obj.__dict__.get(attr_name)
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if old_attribute is not None and isinstance(old_attribute, staticmethod):
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orig_attr = staticmethod(orig_attr)
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self.stubs.append((orig_obj, attr_name, orig_attr))
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setattr(orig_obj, attr_name, new_attr)
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def SmartUnsetAll(self):
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"""Reverses all the SmartSet() calls, restoring things to their original
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definition. Its okay to call SmartUnsetAll() repeatedly, as later calls
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have no effect if no SmartSet() calls have been made.
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"""
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self.stubs.reverse()
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for args in self.stubs:
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setattr(*args)
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self.stubs = []
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def Set(self, parent, child_name, new_child):
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"""Replace child_name's old definition with new_child, in the context
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of the given parent. The parent could be a module when the child is a
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function at module scope. Or the parent could be a class when a class'
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method is being replaced. The named child is set to new_child, while
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the prior definition is saved away for later, when UnsetAll() is called.
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This method supports the case where child_name is a staticmethod or a
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classmethod of parent.
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"""
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old_child = getattr(parent, child_name)
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old_attribute = parent.__dict__.get(child_name)
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if old_attribute is not None:
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if isinstance(old_attribute, staticmethod):
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old_child = staticmethod(old_child)
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elif isinstance(old_attribute, classmethod):
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old_child = classmethod(old_child.im_func)
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self.cache.append((parent, old_child, child_name))
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setattr(parent, child_name, new_child)
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def UnsetAll(self):
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"""Reverses all the Set() calls, restoring things to their original
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definition. Its okay to call UnsetAll() repeatedly, as later calls have
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no effect if no Set() calls have been made.
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"""
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# Undo calls to Set() in reverse order, in case Set() was called on the
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# same arguments repeatedly (want the original call to be last one undone)
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self.cache.reverse()
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for (parent, old_child, child_name) in self.cache:
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setattr(parent, child_name, old_child)
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self.cache = []
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