python - 如何覆盖 MagicMock 子类上的 __getitem__

Question

我们正在模拟一个 3rd 方模块，它有一个带有许多嵌套实例的大型 api。它的各种对象通常通过属性、get() 或字典索引 [] 访问。拥有一个将所有 3 个都视为简单属性访问的灵活模拟将非常方便。

class FlexiMock(MagicMock):
    def get(self, x, default=None): 
        return getattr(self, x, default)

    def __getitem__(self, x):
        return getattr(self, x)


t = FlexiMock(status=1)
assert t.status == 1
assert t.get('status') == 1
assert t['status'] == 1, f"{t['status']} vs 1"

结果:

assert t['status'] == 1, f"{t['status']} vs 1"
AssertionError: <FlexiMock name='mock.__getitem__()' id='140549581528368'> vs 1

这看起来很简单，所以我不确定我做错了什么。

Answer 1

unittest.mock 中的类不能很好地与用户定义的子类一起使用。特别是，unittest.mock.MagicMock 做了一些奇怪的事情。当创建一个新实例时，它会获得自己动态生成的子类，该子类会覆盖几乎所有的魔术方法。您的 __getitem__ 被动态生成的子类中的 __getitem__ 覆盖:

In [1]: from unittest.mock import MagicMock

In [2]: class FlexiMock(MagicMock):
   ...:     def get(self, x, default=None):
   ...:         return getattr(self, x, default)
   ...: 
   ...:     def __getitem__(self, x):
   ...:         return getattr(self, x)
   ...: 

In [3]: t = FlexiMock(status=1)

In [4]: type(t).__mro__
Out[4]: 
(unittest.mock.FlexiMock,
 __main__.FlexiMock,
 unittest.mock.MagicMock,
 unittest.mock.MagicMixin,
 unittest.mock.Mock,
 unittest.mock.CallableMixin,
 unittest.mock.NonCallableMock,
 unittest.mock.Base,
 object)

In [5]: type(t).__dict__                                                                                                                                                                                                         
Out[5]: 
mappingproxy({'__doc__': None,
              '__module__': 'unittest.mock',
              '__pos__': <unittest.mock.MagicProxy at 0x7fcd4506cb80>,
              '__rsub__': <unittest.mock.MagicProxy at 0x7fcd3ffe4d60>,
              '__int__': <unittest.mock.MagicProxy at 0x7fcd3ff40130>,
              '__ifloordiv__': <unittest.mock.MagicProxy at 0x7fcd44084fa0>,
              '__trunc__': <unittest.mock.MagicProxy at 0x7fcd440840a0>,
              '__complex__': <unittest.mock.MagicProxy at 0x7fcd3ffdf160>,
              '__rlshift__': <unittest.mock.MagicProxy at 0x7fcd3ffdf8e0>,
              '__sub__': <unittest.mock.MagicProxy at 0x7fcd3ffdf550>,
              '__delitem__': <unittest.mock.MagicProxy at 0x7fcd3ffdf520>,
              '__matmul__': <unittest.mock.MagicProxy at 0x7fcd3ffd71f0>,
              '__imatmul__': <unittest.mock.MagicProxy at 0x7fcd3ffd95e0>,
              '__rshift__': <unittest.mock.MagicProxy at 0x7fcd3ffd9610>,
              '__gt__': <unittest.mock.MagicProxy at 0x7fcd3ffd9d60>,
              '__round__': <unittest.mock.MagicProxy at 0x7fcd3ffd9ee0>,
              '__idiv__': <unittest.mock.MagicProxy at 0x7fcd3ffd91f0>,
              '__neg__': <unittest.mock.MagicProxy at 0x7fcd3ffc9730>,
              '__fspath__': <unittest.mock.MagicProxy at 0x7fcd3ffc92b0>,
              '__imod__': <unittest.mock.MagicProxy at 0x7fcd4404a5b0>,
              '__rdiv__': <unittest.mock.MagicProxy at 0x7fcd4404a6a0>,
              '__add__': <unittest.mock.MagicProxy at 0x7fcd4404a250>,
              '__aiter__': <unittest.mock.MagicProxy at 0x7fcd4404af70>,
              '__floordiv__': <unittest.mock.MagicProxy at 0x7fcd4404a400>,
              '__xor__': <unittest.mock.MagicProxy at 0x7fcd4404aaf0>,
              '__next__': <unittest.mock.MagicProxy at 0x7fcd4404a850>,
              '__rrshift__': <unittest.mock.MagicProxy at 0x7fcd4404a8b0>,
              '__truediv__': <unittest.mock.MagicProxy at 0x7fcd4404afa0>,
              '__imul__': <unittest.mock.MagicProxy at 0x7fcd4404a070>,
              '__eq__': <unittest.mock.MagicProxy at 0x7fcd3ff8bc70>,
              '__ior__': <unittest.mock.MagicProxy at 0x7fcd3ff8b580>,
              '__enter__': <unittest.mock.MagicProxy at 0x7fcd3ff8b280>,
              '__abs__': <unittest.mock.MagicProxy at 0x7fcd3ff8bdf0>,
              '__le__': <unittest.mock.MagicProxy at 0x7fcd3ff8b4c0>,
              '__rdivmod__': <unittest.mock.MagicProxy at 0x7fcd3ff8ba30>,
              '__getitem__': <unittest.mock.MagicProxy at 0x7fcd3ff8bc10>,
              '__sizeof__': <unittest.mock.MagicProxy at 0x7fcd3ff8b0a0>,
              '__bool__': <unittest.mock.MagicProxy at 0x7fcd3ff8b1f0>,
              '__or__': <unittest.mock.MagicProxy at 0x7fcd3ff8b4f0>,
              '__radd__': <unittest.mock.MagicProxy at 0x7fcd3ff8b730>,
              '__lt__': <unittest.mock.MagicProxy at 0x7fcd3ff8b070>,
              '__rtruediv__': <unittest.mock.MagicProxy at 0x7fcd3ff8b3d0>,
              '__rmatmul__': <unittest.mock.MagicProxy at 0x7fcd3ff8bb20>,
              '__mul__': <unittest.mock.MagicProxy at 0x7fcd3ff8bb80>,
              '__divmod__': <unittest.mock.MagicProxy at 0x7fcd3ff8ba00>,
              '__float__': <unittest.mock.MagicProxy at 0x7fcd3ff8b6a0>,
              '__and__': <unittest.mock.MagicProxy at 0x7fcd3ff8bd00>,
              '__len__': <unittest.mock.MagicProxy at 0x7fcd3ff8bca0>,
              '__ixor__': <unittest.mock.MagicProxy at 0x7fcd3ff8b5e0>,
              '__index__': <unittest.mock.MagicProxy at 0x7fcd3ff8b670>,
              '__aexit__': <unittest.mock.MagicProxy at 0x7fcd3ff8bdc0>,
              '__lshift__': <unittest.mock.MagicProxy at 0x7fcd45062340>,
              '__rfloordiv__': <unittest.mock.MagicProxy at 0x7fcd450628b0>,
              '__ge__': <unittest.mock.MagicProxy at 0x7fcd450622b0>,
              '__irshift__': <unittest.mock.MagicProxy at 0x7fcd45062a90>,
              '__iadd__': <unittest.mock.MagicProxy at 0x7fcd440615b0>,
              '__iter__': <unittest.mock.MagicProxy at 0x7fcd44061790>,
              '__ne__': <unittest.mock.MagicProxy at 0x7fcd440613a0>,
              '__ilshift__': <unittest.mock.MagicProxy at 0x7fcd44061910>,
              '__rpow__': <unittest.mock.MagicProxy at 0x7fcd440614f0>,
              '__ror__': <unittest.mock.MagicProxy at 0x7fcd44061880>,
              '__div__': <unittest.mock.MagicProxy at 0x7fcd440618e0>,
              '__isub__': <unittest.mock.MagicProxy at 0x7fcd44061670>,
              '__hash__': <unittest.mock.MagicProxy at 0x7fcd440617c0>,
              '__rand__': <unittest.mock.MagicProxy at 0x7fcd44061640>,
              '__setitem__': <unittest.mock.MagicProxy at 0x7fcd44061610>,
              '__iand__': <unittest.mock.MagicProxy at 0x7fcd440618b0>,
              '__invert__': <unittest.mock.MagicProxy at 0x7fcd44061760>,
              '__ipow__': <unittest.mock.MagicProxy at 0x7fcd440619d0>,
              '__str__': <unittest.mock.MagicProxy at 0x7fcd44061a30>,
              '__contains__': <unittest.mock.MagicProxy at 0x7fcd44061a90>,
              '__ceil__': <unittest.mock.MagicProxy at 0x7fcd44061040>,
              '__anext__': <unittest.mock.MagicProxy at 0x7fcd44061100>,
              '__exit__': <unittest.mock.MagicProxy at 0x7fcd440610d0>,
              '__floor__': <unittest.mock.MagicProxy at 0x7fcd44061490>,
              '__rmul__': <unittest.mock.MagicProxy at 0x7fcd440613d0>,
              '__mod__': <unittest.mock.MagicProxy at 0x7fcd44061730>,
              '__aenter__': <unittest.mock.MagicProxy at 0x7fcd44061af0>,
              '__pow__': <unittest.mock.MagicProxy at 0x7fcd44061b20>,
              '__rmod__': <unittest.mock.MagicProxy at 0x7fcd44061b80>,
              '__rxor__': <unittest.mock.MagicProxy at 0x7fcd44061be0>,
              '__itruediv__': <unittest.mock.MagicProxy at 0x7fcd44061c40>})

这里，unittest.mock.FlexiMock 是动态生成的子类，带有一个充满魔法方法覆盖的字典。

与其尝试子类化 unittest.mock 类，支持的覆盖方法的 API 只是创建一个常规模拟并在实例上设置方法。请注意，由于额外的 unittest.mock 怪异，魔法方法应该采用 self，但其他方法应该不采用self:

def make_fleximock(*args, **kwargs):
    mock = MagicMock(*args, **kwargs)
    mock.get = lambda x, default=None: getattr(mock, x, default)
    mock.__getitem__ = lambda self, x: getattr(self, x)
    return mock