functools.partial希望使用位置参数作为关键字参数 [英] functools.partial wants to use a positional argument as a keyword argument

问题描述

所以我想了解partial:

import functools

def f(x,y) :
    print x+y

g0 = functools.partial( f, 3 )
g0(1)

4 # Works as expected

在:

g1 = functools.partial( f, y=3 )
g1(1)

4 # Works as expected

在:

g2 = functools.partial( f, x=3 )
g2(1)

TypeError: f() got multiple values for keyword argument 'x'

如果我将y用作关键字参数，则TypeError会消失:

The TypeError disappears if I use y as a keyword argument:

在:

g2( y=1 )

4

什么原因导致TypeError?

推荐答案

这与functools.partial无关.您实质上是这样调用函数的:

This has nothing to do with functools.partial, really. You are essentially calling your function like this:

f(1, x=3)

Python首先满足位置参数，而您的第一个参数是x.然后应用关键字参数，并且您再次 提供了x.

Python first fulfils the positional arguments, and your first argument is x. Then the keyword arguments are applied, and you again supplied x.

functools.partial()无法检测到您已经提供了第一个位置参数作为关键字参数.不会通过用y=关键字参数替换位置参数来增加通话量.

functools.partial() has no means to detect that you already supplied the first positional argument as a keyword argument instead. It will not augment your call by replacing the positional argument with a y= keyword argument.

在混合使用位置参数和关键字参数时，必须注意不要重复使用同一参数.

When mixing positional and keyword arguments, you must take care not to use the same argument twice.

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