new_contents: from collections import Counter
  class Solution(object):
      def findTheDifference(self, s, t):
          """
          :type s: str
          :type t: str
          :rtype: str
          """
          sc, tc = Counter(s), Counter(t)
          for c, v in tc.iteritems():
              if v != sc[c]:
                  return c
  
subject: Add py solution for 389. Find the Difference