code: def header_length(bytearray):
      
      groups_of_3, leftover = divmod(len(bytearray), 3)
      # 4 bytes out for each 3 bytes (or nonzero fraction thereof) in.
      n = groups_of_3 * 4
      if leftover:
          n += 4
      return n
docs: Return the length of s when it is encoded with base64.