Python在捕获循环变量的循环中创建函数 [英] Python create function in a loop capturing the loop variable

问题描述

这是怎么回事?我正在尝试创建一个函数列表:

What's going on here? I'm trying to create a list of functions:

def f(a,b):
    return a*b

funcs = []

for i in range(0,10):
    funcs.append(lambda x:f(i,x))

这不符合我的预期.我希望列表像这样:

This isn't doing what I expect. I would expect the list to act like this:

funcs[3](3) = 9
funcs[0](5) = 0

但是列表中的所有功能似乎都相同，并且将固定值设置为9:

But all the functions in the list seem to be identical, and be setting the fixed value to be 9:

funcs[3](3) = 27
funcs[3](1) = 9

funcs[2](6) = 54

有什么想法吗?

推荐答案

python 中的 lambdas 是闭包......你给它的参数在 lambda 被评估之前不会被评估.那个时候不管i=9，因为你的迭代已经完成了.

lambdas in python are closures.... the arguments you give it aren't going to be evaluated until the lambda is evaluated. At that time, i=9 regardless, because your iteration is finished.

您正在寻找的行为可以通过 functools.partial 实现

The behavior you're looking for can be achieved with functools.partial

import functools

def f(a,b):
    return a*b

funcs = []

for i in range(0,10):
    funcs.append(functools.partial(f,i))

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