code: def __common_triplet(input_string, consonants, vowels):
      
      output = consonants
  
      while len(output) < 3:
          try:
              output += vowels.pop(0)
          except IndexError:
              # If there are less wovels than needed to fill the triplet,
              # (e.g. for a surname as "Fo'" or "Hu" or the corean "Y")
              # fill it with 'X';
              output += 'X'
  
      return output[:3]
docs: __common_triplet(input_string, consonants, vowels) -> string