code: def _trim(cls, s):
          
          reverse = s[::-1]
          idx = 0
          for i in range(0, len(reverse)):
              if reverse[i] == ":":
                  idx += 1
              else:
                  break
  
          # Return the substring after all trailing colons,
          # reversed back to its original character order.
          new_s = reverse[idx: len(reverse)]
          return new_s[::-1]
docs: Remove trailing colons from the URI back to the first non-colon.
  
          :param string s: input URI string
          :returns: URI string with trailing colons removed
          :rtype: string
  
          TEST: trailing colons necessary
  
          >>> s = '1:2::::'
          >>> CPE._trim(s)
          '1:2'
  
          TEST: trailing colons not necessary
  
          >>> s = '1:2:3:4:5:6'
          >>> CPE._trim(s)
          '1:2:3:4:5:6'