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我有一个奇怪的情况，添加显式类型提示似乎会使 mypy 失败。

此代码验证（Python 3.6.1，mypy 0.540）：

class BaseA:
    def __init__(self):
        self.foo: float = 1.0

class DerivedA(BaseA):
    @property
    def foo(self):
        return 2.0

但告诉 mypy 什么属性返回失败

class BaseB:
    def __init__(self):
        self.foo: float = 1.0

class DerivedB(BaseB):
    @property
    def foo(self) -> float:
        return 2.0

# error: Signature of "foo" incompatible with supertype "BaseB"

相关的，我认为，离开注释也会因多重继承而失败，无论哪种组合（两者，任一，无）都被注释：

class BaseC:
    foo: float = 1.0

class MixinC:
    @property
    def foo(self):
        return 2.0

class DerivedC(MixinC, BaseC):
    pass

# error: Definition of "foo" in base class "MixinC" is incompatible with
# definition in base class "BaseC"

任何想法为什么，或者如何改变？

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