human
I found an interesting problem on https://leetcode.com/problems/tag-validator/:
Given a string representing a code snippet, you need to implement a tag validator to parse the code and return whether it is valid. A code snippet is valid if all the following rules hold:

The code must be wrapped in a valid closed tag. Otherwise, the code is invalid.
A closed tag (not necessarily valid) has exactly the following format : <TAG_NAME>TAG_CONTENT</TAG_NAME>. Among them, <TAG_NAME> is the start tag, and </TAG_NAME> is the end tag. The TAG_NAME in start and end tags should be the same. A closed tag is valid if and only if the TAG_NAME and TAG_CONTENT are valid.
A valid TAG_NAME only contain upper-case letters, and has length in range [1,9]. Otherwise, the TAG_NAME is invalid.
A valid TAG_CONTENT may contain other valid closed tags, cdata and any characters (see note1) EXCEPT unmatched <, unmatched start and end tag, and unmatched or closed tags with invalid TAG_NAME. Otherwise, the TAG_CONTENT is invalid.
A start tag is unmatched if no end tag exists with the same TAG_NAME, and vice versa. However, you also need to consider the issue of unbalanced when tags are nested.
A < is unmatched if you cannot find a subsequent >. And when you find a < or </, all the subsequent characters until the next > should be parsed as TAG_NAME  (not necessarily valid).
The cdata has the following format : <![CDATA[CDATA_CONTENT]]>. The range of CDATA_CONTENT is defined as the characters between <![CDATA[ and the first subsequent ]]>. 
CDATA_CONTENT may contain any characters. The function of cdata is to forbid the validator to parse CDATA_CONTENT, so even it has some characters that can be parsed as tag (no matter valid or invalid), you should treat it as regular characters. 

Valid Code Examples:

Input: "<DIV>This is the first line <![CDATA[<div>]]></DIV>"
Output: True
Explanation: 
The code is wrapped in a closed tag : <DIV> and </DIV>. 
The TAG_NAME is valid, the TAG_CONTENT consists of some characters and cdata. 
Although CDATA_CONTENT has unmatched start tag with invalid TAG_NAME, it should be considered as...

I tried it in Python, but could not do it. Can you solve it?

 ... Can you provide a Python program to find a subsequent >?
assistant
#Here is Python program to find a subsequent >.

class Solution:
     def isValid(self, code):
         """
         :type code: str
         :rtype: bool
         """
         S=code
         CDATA_BEGIN='![CDATA['
         CDATA_END=']]>'
         
         
         def collect_tag(i):
             
             for j in range(i,len(S)):
                 if S[j]=='>':
                     break
             else:
                     return None
             return S[i+1:j]
         
         def valid_tag(tag):
             if 1<=len(tag)<=9 and all('A' <=c<= 'Z'  for c in tag):
                 return True
             else:
                 return False
         
         if not S or S[0]!='<':
             return False
         #print('###########1111############')
         tag=collect_tag(0)
         #print(tag)
         if not tag or not S.startswith('<{}>'.format(tag)) or not S.endswith('</{}>'.format(tag)) or not valid_tag(tag):
             
             return False
         
         S=S[len(tag)+2:-len(tag)-3]
         
         
         
         i=0
         stack=[]
         
         while i<len(S):
             
             if S[i]=='<':
                 tag=collect_tag(i)
                 #print(tag)
                 if not tag:
                     
                     return False
                 
                 if tag.startswith(CDATA_BEGIN):
                     while i<len(S)  and S[i:i+3]!=CDATA_END:
                         i+=1
                     if S[i:i+3]!=CDATA_END:
                         return False
                     i+=2
                 elif tag.startswith('/'):
                     tag=tag[1:]
                     if  not valid_tag(tag) or not stack or stack.pop()!=tag:
                         return False
                 else:
                     if not valid_tag(tag):
                         return False
                     stack.append(tag)
            
             i+=1
         return not stack