Leetcode408.Valid Word Abbreviation

def validWordAbbreviation(word, abbr):
    i, j = 0, 0
    while i < len(abbr):
        if j >= len(word):
            return False
        if not abbr[i].isdigit():
            if abbr[i] != word[j]:
                return False
            i += 1
            j += 1
        else:
            if abbr[i] == '0':
                return False
            n = ''
            while i < len(abbr) and abbr[i].isdigit():
                n += abbr[i]
                i +=1
            j += int(n)
    return j==len(word)

s = 'internationalization'
a = 'i12iz4n'
print(validWordAbbreviation(s,a))