docs: def find_common(self, l):
          """
          Find common parts in thelist items ex: 'ab' for ['abcd','abce','abf']
          requires an ordered list
          """
          if len(l) == 1:
              return l[0]
  
          init = l[0]
          for item in l[1:]:
              for i, (x, y) in enumerate(zip(init, item)):
                  if x != y:
                      init = "".join(init[:i])
                      break
  
              if not init:
                  return None
          return init