Python的带下划线的lambda作为参数?

问题描述

以下代码是做什么的?

a = lambda _:True

根据我在交互式提示中阅读和测试的内容，它似乎是一个始终返回True的函数.

From what I read and tested in the interactive prompt, it seems to be a function that returns always True.

我理解正确吗?我希望了解为什么还要使用下划线(_).

Am I understanding this correctly? I hope to understand why an underscore (_) was used as well.

推荐答案

_是变量名.试试吧.(此变量名称通常是忽略变量的名称.可以说是占位符.)

The _ is variable name. Try it.(This variable name is usually a name for an ignored variable. A placeholder so to speak.)

Python:

>>> l = lambda _: True
>>> l()
<lambda>() missing 1 required positional argument: '_'

>>> l("foo")
True

因此，此lambda 需要一个参数.如果您想要一个不带参数的lambda 始终返回True，请执行以下操作:

So this lambda does require one argument. If you want a lambda with no argument that always returns True, do this:

>>> m = lambda: True
>>> m()
True

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