Question

在第7章中，作者创建了一个迭代器，用于构建将单数英语名词转换为复数的规则：

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()

虽然本书对此代码的每一部分提供了非常明确和详尽的解释，但它并没有解释如何使用它？ 如何使用这些规则更改名词？

我尝试将这一位添加到课程中：

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))

更新：我将代码更改为 janos 中的评论。所以它现在看起来像这样：

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))

它现在有效!!!!谢谢 janos ！

但是，我还有另一个问题：为什么在build_match_and_apply_functions()函数matches_rule(word)中有一个变量＆＃39; word＆＃39; ，而在the plural()函数中matches_rule(noun)有一个变量＆＃39;名词＆＃39; ，不应该将变量命名为相同？

Answer 1

plural不应该是LazyRules的方法，而应该是一个独立的函数。它应该发布rules（这是自定义迭代器类LazyRules的一个实例）：

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))

深入Python第7章：我如何使用这个迭代器？

1 个答案: