LeetCode "468. Validate IP Address"

it is all about corner-cases...

class Solution(object):
    def validIP4(self, IP):
        def validNum4(s):
            try: 
                # leading zero, negative
                if (s[0] == '0' and len(s) > 1) or s[0] == '-':
                    return False
                # value range
                v = int(s)
                if not (v >= 0 and v <= 255):
                    return False
            except ValueError:
                return False
            return True
            
        arr = IP.split(".")
        for s in arr:
            if len(s) == 0:
                return False
            if not validNum4(s):
                return False
        return True
        
    def validIP6(self, IP):
        def validNum6(s):
            s = s.lower()
            for c in s:
                if not ((c >= '0' and c <= '9') or (c >= 'a' and c <= 'f')):
                    return False
            return True
            
        arr = IP.split(":")
        for s in arr:
            if len(s) == 0 or len(s) > 4:
                return False
                
            if not validNum6(s):
                return False
        return True
        
    def validIPAddress(self, IP):
        """
        :type IP: str
        :rtype: str
        """
        bIs4 = len(IP.split(".")) == 4
        if bIs4:
            if self.validIP4(IP):
                return "IPv4"
        bIs6 = len(IP.split(":")) == 8
        if bIs6:
            if self.validIP6(IP):
                return "IPv6"
        return "Neither"