code: def _readoct(self, length, start):
          
          if length % 3:
              raise InterpretError("Cannot convert to octal unambiguously - "
                                   "not multiple of 3 bits.")
          if not length:
              return ''
          # Get main octal bit by converting from int.
          # Strip starting 0 or 0o depending on Python version.
          end = oct(self._readuint(length, start))[LEADING_OCT_CHARS:]
          if end.endswith('L'):
              end = end[:-1]
          middle = '0' * (length // 3 - len(end))
          return middle + end
docs: Read bits and interpret as an octal string.