code: def pept_diff(p1, p2):
      
      if len(p1) != len(p2):
          return -1
      else:
          return sum([p1[i] != p2[i] for i in range(len(p1))])
docs: Return the number of differences betweeen 2 peptides
  
      :param str p1: Peptide 1
      :param str p2: Peptide 2
      :return: The number of differences between the pepetides
      :rtype: int
  
      >>> pept_diff('ABCDE', 'ABCDF')
      1
      >>> pept_diff('ABCDE', 'ABDFE')
      2
      >>> pept_diff('ABCDE', 'EDCBA')
      4
      >>> pept_diff('ABCDE', 'ABCDE')
      0