code: def seek(self, offset, whence=0):
          
          self._check_open_file()
          if not self._append:
              self._io.seek(offset, whence)
          else:
              self._read_seek = offset
              self._read_whence = whence
          if not self.is_stream:
              self.flush()
docs: Move read/write pointer in 'file'.