深入Python第7章：如何使用此迭代器？

Question

在第7章中，作者創建了一個迭代器，該迭代器構建了將單數英語名詞轉換為復數形式的規則：

class LazyRules:

        rules_filename = 'plural5-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()

盡管本書對這段代碼的每一部分都提供了非常清晰而透徹的解釋，但並未解釋如何使用它？ 如何使用這些規則更改名詞？

我試圖將此添加到類中：

def build_match_and_apply_functions(self, 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)

def plural(self, noun):
      for matches_rule, apply_rule in self.__next__():
         if matches_rule(noun):
            return apply_rule(noun)
      raise ValueError('no matching rule for {0}'.format(noun))

Upd：我更改了janos注釋中添加的代碼。 所以現在看起來像這樣：

class LazyRules:
        rules_filename = 'plural5-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()

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)

def plural(noun):
      for matches_rule, apply_rule in rules:
         if matches_rule(noun):
            return apply_rule(noun)
      raise ValueError('no matching rule for {0}'.format(noun))

現在就可以使用！！！ 謝謝janos ！

但是，我還有一個問題：為什么在build_match_and_apply_functions()函數中， matches_rule(word)具有變量'word' ，而在the plural()函數中， matches_rule(noun)具有變量'noun' ，該變量不應命名為相同？

Answer 1

plural不應是LazyRules的方法，而應是獨立的功能。 它應該發出rules （這是自定義迭代器類LazyRules的實例）：

def plural(self, noun):
      for matches_rule, apply_rule in rules:
         if matches_rule(noun):
            return apply_rule(noun)
      raise ValueError('no matching rule for {0}'.format(noun))