code: def get_extra(descriptor):
      
      result = []
      extra_length = descriptor.extra_length
      if extra_length:
          extra = buffer_at(descriptor.extra.value, extra_length)
          append = result.append
          while extra:
              length = _string_item_to_int(extra[0])
              if not 0 < length <= len(extra):
                  raise ValueError(
                      'Extra descriptor %i is incomplete/invalid' % (
                          len(result),
                      ),
                  )
              append(extra[:length])
              extra = extra[length:]
      return result
docs: Python-specific helper to access "extra" field of descriptors,
      because it's not as straight-forward as in C.
      Returns a list, where each entry is an individual extra descriptor.