Leetcode: Plus One @Python

class Solution:
    # @param digits, a list of integer digits
    # @return a list of integer digits
    def plusOne(self, digits):
        n=len(digits)
        if n==0:
            return [1]
        i=n-1
        while i>=0:
            if digits[i]+1<10:
                digits[i]+=1
                return digits
            digits[i]=0
            i-=1
        digits.insert(0,1)
        return digits