《Python基础教程》第三版第20章“自动添加标签”项目输出结果重复的问题

   学习《Python基础教程》第三版，到第20章“自动添加标签”项目，从官网下载了源代码运行，发现输出的test_output.html中每一行内容都重复了三次。下载了第二版的代码 比较后发现第三版代码和书中代码都有一个小bug，markup.py里parse函数中for rule in self.rules:一句向后缩进了4格导致进入了上一个循环。修正后的代码如下：

import sys, re
from handlers import *
from util import *
from rules import *


class Parser:
    """
    A Parser reads a text file, applying rules and controlling a handler.
    """
    def __init__(self, handler):
        self.handler = handler
        self.rules = []
        self.filters = []

    def addRule(self, rule):
        self.rules.append(rule)

    def addFilter(self, pattern, name):
        def filter(block, handler):
            return re.sub(pattern, handler.sub(name), block)
        self.filters.append(filter)

    def parse(self, file):
        self.handler.start('document')
        for block in blocks(file):
            for filter in self.filters:
                block = filter(block, self.handler)
            for rule in self.rules:
                if rule.condition(block):
                    if rule.action(block, self.handler): break
        self.handler.end('document')


class BasicTextParser(Parser):
    """
    A specific Parser that adds rules and filters in its constructor.
    """
    def __init__(self, handler):
        Parser.__init__(self, handler)
        self.addRule(ListRule())
        self.addRule(ListItemRule())
        self.addRule(TitleRule())
        self.addRule(HeadingRule())
        self.addRule(ParagraphRule())

        self.addFilter(r'\*(.+?)\*', 'emphasis')
        self.addFilter(r'(http://[\.a-zA-Z/]+)', 'url')
        self.addFilter(r'([\.a-zA-Z]+@[\.a-zA-Z]+[a-zA-Z]+)', 'mail')


handler = HTMLRenderer()
parser = BasicTextParser(handler)
# file = open('test_input.txt','r')
# parser.parse(file)
parser.parse(sys.stdin)

#python markup.py < test_input.txt > test_output.html