将布尔值与整数混合时，Mypy 不会抛出错误

2022-01-19 00:00:00 python integer mypy boolean

问题描述

我正在尝试使用 mypy 来检查 Python 3 项目.在下面的示例中，我希望 mypy 将类 MyClass 的构造标记为错误，但事实并非如此.

I am trying to use mypy to check a Python 3 project. In the example below, I want mypy to flag the construction of the class MyClass as an error, but it doesn't.

class MyClass:
    def __init__(self, i:int) -> None:
        pass

obj = MyClass(False)

谁能解释一下，好吗?IE.解释一下mypy为什么不报错?

Can anyone explain this, please? I.e. explain why mypy does not report an error?

解决方案

这是因为——不幸的是！— Python 中的布尔值是整数.如，bool 是 int 的子类:

It’s because — unfortunately! — booleans in Python are integers. As in, bool is a subclass of int:

In [1]: issubclass(bool, int)
Out[1]: True

因此代码类型检查，并且 False 是一个有效的整数，值为 0.

Hence the code typechecks, and False is a valid integer with value 0.

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