带有嵌套函数作用域的 UnboundLocalError [英] UnboundLocalError with nested function scopes

问题描述

我有这样的代码(简化):

I have code like this (simplified):

def outer():
    ctr = 0

    def inner():
        ctr += 1

    inner()

但是 ctr 导致错误:

Traceback (most recent call last):
  File "foo.py", line 9, in <module>
    outer()
  File "foo.py", line 7, in outer
    inner()
  File "foo.py", line 5, in inner
    ctr += 1
UnboundLocalError: local variable 'ctr' referenced before assignment

我该如何解决这个问题?我认为嵌套范围可以让我这样做.我试过全局"，但它仍然不起作用.

How can I fix this? I thought nested scopes would have allowed me to do this. I've tried with 'global', but it still doesn't work.

推荐答案

如果您使用的是 Python 3，则可以使用 nonlocal 语句启用重新绑定非本地名称:

If you're using Python 3, you can use the nonlocal statement to enable rebinding of a nonlocal name:

def outer():
    ctr = 0

    def inner():
        nonlocal ctr
        ctr += 1

    inner()

如果您使用的 Python 2 没有 nonlocal，则需要在不重新绑定裸名的情况下执行递增(通过将计数器保留为某个裸名的项目或属性， 不 作为一个裸名本身).例如:

If you're using Python 2, which doesn't have nonlocal, you need to perform your incrementing without barename rebinding (by keeping the counter as an item or attribute of some barename, not as a barename itself). For example:

...
ctr = [0]

def inner():
    ctr[0] += 1
...

当然，现在在其他地方使用裸 ctr 的任何地方都使用 ctr[0].

and of course use ctr[0] wherever you're using bare ctr now elsewhere.

这篇关于带有嵌套函数作用域的 UnboundLocalError的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！