substring html code without html breaking

gistfile1.sh

adylab:script adyliu$ python3 htmlsubstring.py 
<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span><div>我靠，我就不信不行</div><h2>标题党</h2></div>
<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span></div>
<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span></div>

<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span><div>我靠，</div></div>
<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span><div>我靠，</div></div>

<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span><div>我靠，我就不</div></div>
<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span><div>我靠，我就不</div></div>

<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span><div>我靠，我就不信不行</div></div>
<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span><div>我靠，我就不信不行</div></div>

htmlsubstring.py

#!/usr/bin/env python3
#-*- coding: utf-8 -*-
#substring html code without html breaking
#author: Ady Liu(http://github.com/adyliu)
#date: 2012-12-28



notags=('img','br','hr')

class Tag():
    def __init__(self,label,pre=None):
        self.pre=pre
        self.label=label
        self.end=False
    def __str__(self):
        return self.label+':'+str(self.end)
    def __repr__(self):
        return self.__str__()

def substring2(html,size):
    if len(html) <= size:
        return html
    result,tag,count='','',0,0
    tags=[]
    for c in html:
        result += c
        if c == '<':
            intag=True
        elif c=='>':
            intag=False
            tag=tag.split()[0]
            if tag[0] == '/':
                tag = tag.replace('/','')
                if tag not in notags:
                    tags.pop()
            else:
                if tag[-1] != '/' and tag not in notags:
                    tags.append(tag)
            tag=''
        else:
            if intag: 
                tag += c
            else:
                count+=1
                if count>=size: break
    while len(tags)>0:
        result += '</{0}>'.format(tags.pop())
    return result


def substring(html,size):
    if len(html) <= size:
        return html

    result=''
    offset,count=0,0
    tags=[]
    tag=''
    cur=None
    for c in html:
        result += c
        offset += 1
        if c=='<':
            intag=True
        elif c=='>':
            intag=False
            tag=tag.split()[0]
            if tag[-1] == '/': tag=tag[0:-1]
            if tag[0] == '/':
                tag = tag[1:]
                if tag not in notags:
                    while cur:
                        if cur.label == tag and not cur.end:
                            cur.end=True
                            break
                        cur=cur.pre
            else:
                if tag not in notags:
                    t = Tag(tag,cur)
                    tags.append(t)
                    cur = t
            tag=''
        else:
            if intag:
                tag+=c
            else:
                count+=1
                if count>=size:break
    #print('tags',tags)
    for t in reversed(tags):
        if not t.end:
            result += '</{0}>'.format(t.label)

    return result

if __name__ == '__main__':
    s='<div class="test">测试<span>谁知道&amp;<br>是<br/>什么<br />东东<i>也许吧</i></span><div>我靠，我就不信不行</div><h2>标题党</h2></div>'
    
    for i in range(18,30):
        print(s)
        print(substring(s,i))
        print(substring2(s,i))
        print()