Python Lambda和作用域 [英] Python lambdas and scoping

问题描述

给出以下代码段:

funcs = []
for x in range(3):
    funcs.append(lambda: x)
print [f() for f in funcs]

我希望它会打印[0, 1, 2]，但是会打印[2, 2, 2].关于lambda如何与作用域一起工作，我是否缺少一些基本的知识?

I would expect it to print [0, 1, 2], but instead it prints [2, 2, 2]. Is there something fundamental I'm missing about how lambdas work with scope?

推荐答案

这是Python中的常见问题.基本上，作用域是这样的:调用f()时，它将使用x的当前值，而不是形成lambda时的x值.有一个标准的解决方法:

This is a frequent question in Python. Basically the scoping is such that when f() is called, it will use the current value of x, not the value of x at the time the lambda is formed. There is a standard workaround:

funcs = []
for x in range(10):
funcs.append(lambda x=x: x)
print [f() for f in funcs]

使用lambda x = x检索并保存x的当前值.

The use of lambda x = x retrieves and saves the current value of x.

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