python leetcode 38. Count and Say

# The count-and-say sequence is the sequence of integers with the first five terms as following:
# 1.     1
# 2.     11
# 3.     21
# 4.     1211
# 5.     111221
# 1 is read off as "one 1" or 11.
# 11 is read off as "two 1s" or 21.
# 21 is read off as "one 2, then one 1" or 1211.
# Given an integer n where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence.
# Note: Each term of the sequence of integers will be represented as a string.
"""
Input: 1    Output: "1"
Input: 4    Output: "1211"
"""
class Solution(object):
    def countAndSay(self, n):
        """
        :type n: int
        :rtype: str
        """
        seq = '1'
        for i in range(n - 1):
            seq = self.getnext(seq)
        return seq

    def getnext(self, seq):
        nextseq = ''
        i = 0
        while i < len(seq):
            cnt = 1
            while i < len(seq) - 1 and seq[i] == seq[i + 1]:
                cnt += 1
                i += 1
            nextseq += (str(cnt) + seq[i])
            i += 1
        return nextseq