正斜杠“/"是什么意思?在 Python 方法签名中，如 help(foo) 所示? [英] What is the meaning of a forward slash "/" in a Python method signature, as shown by help(foo)?

问题描述

在help(foo)交互返回的签名中，一个/是什么意思?

In the signature returned interactively by help(foo), what is the meaning of a /?

In [37]: help(object.__eq__)

Help on wrapper_descriptor:

__eq__(self, value, /)
    Return self==value.

In [55]: help(object.__init__)

Help on wrapper_descriptor:

__init__(self, /, *args, **kwargs)
    Initialize self.  See help(type(self)) for accurate signature.

我认为这可能与仅关键字参数有关，但事实并非如此.当我使用仅关键字参数创建自己的函数时，位置参数和仅关键字参数由 *(如预期)分隔，而不是由 / 分隔./ 是什么意思?

I thought it might be related to keyword-only arguments, but it's not. When I create my own function with keyword-only arguments, positional and keyword-only arguments are separated by * (as expected), not by /. What does the / mean?

推荐答案

如此处所述，/"为参数标记仅位置参数的结束(参见 此处)，即不能用作关键字参数的参数.在 __eq__(self, value,/) 的情况下，斜线在末尾，这意味着所有参数仅在 __init__ 的情况下被标记为位置只有自我，即没有，只是位置.

As explained here, the '/' as an argument marks the end of arguments that are positional only (see here), i.e. arguments you can't use as keyword parameters. In the case of __eq__(self, value, /) the slash is at the end, which means that all arguments are marked as positional only while in the case of your __init__ only self, i.e. nothing, is positional only.

这以前仅用于内置函数，但 自 Python 3.8 起，你可以在你自己的函数中使用它.\ 的自然伴侣是 * ，它允许标记仅关键字参数的开头.使用两者的示例:

This was previously only used for built-in functions but since Python 3.8, you can use this in your own functions. The natural companion of \ is * which allows to mark the beginning of keyword-only arguments. Example using both:

# a, b are positional-only. e,f keyword-only
def f(a, b, /, c, d, *, e, f): 
    print(a, b, c, d, e, f)

# valid call
f(10, 20, 30, d=40, e=50, f=60)

# invalid calls:
f(10, b=20, c=30, d=40, e=50, f=60)   # b cannot be a keyword argument
f(10, 20, 30, 40, 50, f=60)           # e must be a keyword argument

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