third_party/protobuf/python/stubout.py

   1 #!/usr/bin/python2.4
   2 #
   3 # Copyright 2008 Google Inc.
   4 #
   5 # Licensed under the Apache License, Version 2.0 (the "License");
   6 # you may not use this file except in compliance with the License.
   7 # You may obtain a copy of the License at
   8 #
   9 #      http://www.apache.org/licenses/LICENSE-2.0
  10 #
  11 # Unless required by applicable law or agreed to in writing, software
  12 # distributed under the License is distributed on an "AS IS" BASIS,
  13 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14 # See the License for the specific language governing permissions and
  15 # limitations under the License.
  16
  17 # This file is used for testing.  The original is at:
  18 #   http://code.google.com/p/pymox/
  19
  20 class StubOutForTesting:
  21   """Sample Usage:
  22      You want os.path.exists() to always return true during testing.
  23
  24      stubs = StubOutForTesting()
  25      stubs.Set(os.path, 'exists', lambda x: 1)
  26        ...
  27      stubs.UnsetAll()
  28
  29      The above changes os.path.exists into a lambda that returns 1.  Once
  30      the ... part of the code finishes, the UnsetAll() looks up the old value
  31      of os.path.exists and restores it.
  32
  33   """
  34   def __init__(self):
  35     self.cache = []
  36     self.stubs = []
  37
  38   def __del__(self):
  39     self.SmartUnsetAll()
  40     self.UnsetAll()
  41
  42   def SmartSet(self, obj, attr_name, new_attr):
  43     """Replace obj.attr_name with new_attr. This method is smart and works
  44        at the module, class, and instance level while preserving proper
  45        inheritance. It will not stub out C types however unless that has been
  46        explicitly allowed by the type.
  47
  48        This method supports the case where attr_name is a staticmethod or a
  49        classmethod of obj.
  50
  51        Notes:
  52       - If obj is an instance, then it is its class that will actually be
  53         stubbed. Note that the method Set() does not do that: if obj is
  54         an instance, it (and not its class) will be stubbed.
  55       - The stubbing is using the builtin getattr and setattr. So, the __get__
  56         and __set__ will be called when stubbing (TODO: A better idea would
  57         probably be to manipulate obj.__dict__ instead of getattr() and
  58         setattr()).
  59
  60        Raises AttributeError if the attribute cannot be found.
  61     """
  62     if (inspect.ismodule(obj) or
  63         (not inspect.isclass(obj) and obj.__dict__.has_key(attr_name))):
  64       orig_obj = obj
  65       orig_attr = getattr(obj, attr_name)
  66
  67     else:
  68       if not inspect.isclass(obj):
  69         mro = list(inspect.getmro(obj.__class__))
  70       else:
  71         mro = list(inspect.getmro(obj))
  72
  73       mro.reverse()
  74
  75       orig_attr = None
  76
  77       for cls in mro:
  78         try:
  79           orig_obj = cls
  80           orig_attr = getattr(obj, attr_name)
  81         except AttributeError:
  82           continue
  83
  84     if orig_attr is None:
  85       raise AttributeError("Attribute not found.")
  86
  87     # Calling getattr() on a staticmethod transforms it to a 'normal' function.
  88     # We need to ensure that we put it back as a staticmethod.
  89     old_attribute = obj.__dict__.get(attr_name)
  90     if old_attribute is not None and isinstance(old_attribute, staticmethod):
  91       orig_attr = staticmethod(orig_attr)
  92
  93     self.stubs.append((orig_obj, attr_name, orig_attr))
  94     setattr(orig_obj, attr_name, new_attr)
  95
  96   def SmartUnsetAll(self):
  97     """Reverses all the SmartSet() calls, restoring things to their original
  98     definition.  Its okay to call SmartUnsetAll() repeatedly, as later calls
  99     have no effect if no SmartSet() calls have been made.
 100
 101     """
 102     self.stubs.reverse()
 103
 104     for args in self.stubs:
 105       setattr(*args)
 106
 107     self.stubs = []
 108
 109   def Set(self, parent, child_name, new_child):
 110     """Replace child_name's old definition with new_child, in the context
 111     of the given parent.  The parent could be a module when the child is a
 112     function at module scope.  Or the parent could be a class when a class'
 113     method is being replaced.  The named child is set to new_child, while
 114     the prior definition is saved away for later, when UnsetAll() is called.
 115
 116     This method supports the case where child_name is a staticmethod or a
 117     classmethod of parent.
 118     """
 119     old_child = getattr(parent, child_name)
 120
 121     old_attribute = parent.__dict__.get(child_name)
 122     if old_attribute is not None and isinstance(old_attribute, staticmethod):
 123       old_child = staticmethod(old_child)
 124
 125     self.cache.append((parent, old_child, child_name))
 126     setattr(parent, child_name, new_child)
 127
 128   def UnsetAll(self):
 129     """Reverses all the Set() calls, restoring things to their original
 130     definition.  Its okay to call UnsetAll() repeatedly, as later calls have
 131     no effect if no Set() calls have been made.
 132
 133     """
 134     # Undo calls to Set() in reverse order, in case Set() was called on the
 135     # same arguments repeatedly (want the original call to be last one undone)
 136     self.cache.reverse()
 137
 138     for (parent, old_child, child_name) in self.cache:
 139       setattr(parent, child_name, old_child)
 140     self.cache = []