Code

class Solution(object):
    def mergeAlternately(self, word1, word2):
        """
        :type word1: str
        :type word2: str
        :rtype: str
        """
        index = 0
        result = ""
        while index < len(word1):
            result = result + word1[index] + word2[index]
            index += 1
            if index >= len(word1):
                result += word2[index:]
                return result
            if index >= len(word2):
                result += word1[index:]
                return result
        return result