**遍历我所定义的规则，来处理实时读进来的文本，利用condition判断当前规则，可以用来作代码高亮处理 **
1.提供固定的HTML标记的输出（start & end） 2.对标记输出的start end提供友好的访问接口
class Handler: def callback(self, prefix, name, *args): method = getattr(self, prefix + name, None) if callable(method):return method(*args) def start(self, name): self.callback('start_', name) def end(self, name): self.callback('end_', name) def sub(self, name): def substation(match): result = self.callback('sub_', name, match) if result is 'None': match.group(0) return result return substation class HTMLRenderer(Handler): def start_document(self): print('<html><head><title>...</title></head><body') def end_document(self): print('</body></html>') def start_paragraph(self): print('<p>') def end_paragraph(self): print ('</p>') def start_heading(self): print ( '<h2>') def end_heading(self): print ('</h2>') def start_list(self): print ('<ul>') def end_list(self): print ('</ul>') def start_listitem(self): print ('<li>') def end_listitem(self): print ('</li>') def start_title(self): print ('<h1>') def end_title(self): print ( '</h1>') def sub_emphasis(self, match): return '<em>%s</em>' % match.group(1) def sub_url(self, match): return '<a href="%s">%s</a>' % (match.group(1), match.group(1)) def sub_mail(self, match): return '<a href="mailto:%s">%s</a>' % (match.group(1), match.group(1)) def feed(self, data): print(data) if __name__ == '__main__': callable(callable)由正则表达式组成的过滤器 1.强调过滤器（用×号标出的） 2.url过滤器 3.email过滤器
self.addFilter(r'\*(.+?)\*', 'emphasis') self.addFilter(r'(http://[\.a-z0-9A-Z/]+)', 'url') self.addFilter(r'([\.a-zA-Z]+@[\.a-zA-Z]+[a-zA-Z]+)','mail')主要有两个方法，condition & action condition：用来判断读入的字符串是否符合我们的规则 action：用来执行，调用处理程序模块，输出前标签，内容，后标签
class Rule: def action(self, block, handler): handler.start(self.type) handler.feed(block) handler.end(self.type) return True class HeadingRule(Rule): type = 'heading' def condition(self, block): return not '\n' in block and len(block) <= 70 and not block[-1] == ':' class TitleRule(HeadingRule): type = 'title' first = True def condition(self, block): if not self.first: return False self.first = False return HeadingRule.condition(self, block) class ListItemRule(Rule): type = 'listitem' def condition(self, block): return block[0] == '-' def action(self, block, handler): handler.start(self.type) handler.feed(block[1:].strip()) handler.end(self.type) return True class ListRule(ListItemRule): type = 'list' inside = False def condition(self, block): return True def action(self,block, handler): if not self.inside and ListItemRule.condition(self,block): handler.start(self.type) self.inside = True elif self.inside and not ListItemRule.condition(self,block): handler.end(self.type) self.inside = False return False class ParagraphRule(Rule): type = 'paragraph' def condition(self, block): return True协调读入的文本和其他模块的关系，提供了两个存放规则和过滤器的列表，使得规则和过滤器可以动态改变。
import sys, re from Handler import * from uilts import * from rules import * class Parser: 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): last = rule.action(block, self.handler) if last:break self.handler.end('document') class BasicTextParser(Parser): 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-z0-9A-Z/]+)', 'url') self.addFilter(r'([\.a-zA-Z]+@[\.a-zA-Z]+[a-zA-Z]+)','mail') handler = HTMLRenderer() parser = BasicTextParser(handler) parser.parse(sys.stdin)