需要帮助理解Python闭包

问题描述

我有这个代码：

import re

def doReplace(toReplace):
    i = 1
    def chapterReplacer(_):
        result = 'Chapter %i' % i
        i += 1
        return result

    return re.sub('Chapter [a-zA-Z]+', chapterReplacer, test)

test = 'Chapter one Chapter Two Chapter three'
print doReplace(test)

当我运行它，我得到以下错误：

when I run it, I get the following error:

Traceback (most recent call last):
  File "C:/Python26/replace.py", line 13, in <module>
    print doReplace(test)
  File "C:/Python26/replace.py", line 10, in doReplace
    return re.sub('Chapter [a-zA-Z]+', chapterReplacer, test)
  File "C:\Python26\lib\re.py", line 151, in sub
    return _compile(pattern, 0).sub(repl, string, count)
  File "C:/Python26/replace.py", line 6, in chapterReplacer
    result = 'Chapter %i' % i
UnboundLocalError: local variable 'i' referenced before assignment

我的印象是chapterReplacer会捕获局部变量i，

I was under the impression that chapterReplacer would capture the local variable i, but that doesn't seem to be happening?

推荐答案

您可以使 i 函数属性

def doReplace(toReplace):
    chapterReplacer.i = 1
    def chapterReplacer(_):
        result = 'Chapter %i' % chapterReplacer.i
        chapterReplacer.i += 1
        return result

    return re.sub('Chapter [a-zA-Z]+', chapterReplacer, test)

编辑：从python 3开始，可以使用 nonlocal a la @MartijnPieters的解决方案。

As of python 3, you can use nonlocal a la @MartijnPieters 's solution.

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