来自深入Python 3的迭代器示例

我正在学习Python作为我的第一语言。在CHP7上，有一个如何使用迭代器的示例

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“for matches\u规则，apply\u rule in rules:”循环如何知道在满足if条件后何时退出？对于该条件，没有StopIteration命令。我希望for循环继续，直到rules.cache完全迭代

---

谢谢你的帮助

return语句在该点结束函数，向调用者返回一个值。这在几乎任何情况下都可以依赖（如果您有

try..except..else..finally

结构，即使是

return

语句也不会阻止执行

finally

块）