python - 单元测试 : patching an objects __base__

Question

从 this question 开始，我试图用 Mock() 修补类 A() ，这样当 B() 被初始化时，Mock 被用作基础例如:

class A(object): ...
class B(A): ...

def setUp(self):
    with patch('A', new_callable=Mock) as MockObject:
        self.b = B()
        self.b.__class__.__base__ = MockOjbect

这不起作用，因为 base 是只读的。执行此操作的正确方法是什么？

更新:

>>> from mock import Mock
>>> class A(object):
...     pass
... 
>>> class B(A):
...     pass
... 
>>> b.__class__.__bases__ = (Mock, )
>>> b.__class__.__bases__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/envs/myenv/local/lib/python2.7/site-packages/mock.py", line 656, in __getattr__
    elif self._mock_methods is not None:
  File "/opt/envs/myenv/local/lib/python2.7/site-packages/mock.py", line 655, in __getattr__
    raise AttributeError(name)
AttributeError: _mock_methods

需要明确的是，我不相信这是实现我想要做的事情的最佳方式，我有一半希望其他人会想出另一种方式。

Answer 1

__bases__ 是一个元组。

更正版本:

class A(object): ...
class B(A): ...

def setUp(self):
    with patch('A', new_callable=Mock) as MockObject:
        self.b = B()
        self.b.__class__.__bases__ = (MockOjbect,)

参见:

>>> class Foo(object):
...     pass
... 
>>> Foo.__class__.__bases__
(<type 'object'>,)

tuple 是不可变的，但 __bases__ 属性肯定不是只读的。