code: def _get_len(self):
          
          if hasattr(self._buffer, 'len'):
              self._len = self._buffer.len
  
              return
  
          old_pos = self._buffer.tell()
          self._buffer.seek(0, 2)
  
          self._len = self._buffer.tell()
          self._buffer.seek(old_pos)
docs: Return total number of bytes in buffer.