Dive Into Python 3中的迭代器示例 [英] Iterator example from Dive Into Python 3

问题描述

我正在从 http://www.diveintopython3.net/中学习Python作为第一语言.在第7章中， http://www.diveintopython3.net/iterators.html 中有一个使用迭代器的示例.

I'm learning Python as my 1st language from http://www.diveintopython3.net/. On Chp 7, http://www.diveintopython3.net/iterators.html, there is an example of how to use an iterator.

import re

def build_match_and_apply_functions(pattern, search, replace):
    def matches_rule(word):
        return re.search(pattern, word)
    def apply_rule(word):
        return re.sub(search, replace, word)
    return [matches_rule, apply_rule]

class LazyRules:
    rules_filename = 'plural6-rules.txt'

    def __init__(self):
        self.pattern_file = open(self.rules_filename, encoding='utf-8')
        self.cache = []

    def __iter__(self):
        self.cache_index = 0
        return self

    def __next__(self):
        self.cache_index += 1
        if len(self.cache) >= self.cache_index:
            return self.cache[self.cache_index - 1]

        if self.pattern_file.closed:
            raise StopIteration

        line = self.pattern_file.readline()
        if not line:
            self.pattern_file.close()
            raise StopIteration

        pattern, search, replace = line.split(None, 3)
        funcs = build_match_and_apply_functions(
            pattern, search, replace)
        self.cache.append(funcs)
        return funcs

rules = LazyRules()

def plural(noun):
    for matches_rule, apply_rule in rules:
        if matches_rule(noun):
            return apply_rule(noun)

if __name__ == '__main__':
    import sys
    if sys.argv[1:]:
        print(plural(sys.argv[1]))
    else:
        print(__doc__)

我的问题是:复数(名词)函数中的对于matchs_rule，apply_rule在规则中:"循环如何满足if条件后何时退出?没有针对该条件的StopIteration命令.我希望for循环会继续进行，直到rules.cache完全迭代为止.

My question is: how does the 'for matches_rule, apply_rule in rules:' loop in the plural(noun) function know when to exit after fulfilling the if condition? There are no StopIteration commands for that condition. I would expect the for loop to continue until the rules.cache is iterated completely.

谢谢您的帮助！

推荐答案

return语句在该点结束函数，将值返回给调用方.几乎在任何情况下都可以使用它(如果您具有try..except..else..finally结构，即使return语句也不会阻止执行finally块).

The return statement ends the function at that point, returning a value to the caller. This can be relied upon in almost any situation (if you have a try..except..else..finally structure, even a return statement won't prevent the finally block from being executed).

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