def _lookup(self, key=None):
        """Return (start, stop) or raise KeyError."""
        if self._toc is None:
            self._generate_toc()
        if key is not None:
            try:
                return self._toc[key]
            except KeyError:
                raise KeyError('No message with key: %s' % key)
dataset/ETHPy150Open babble/babble/include/jython/Lib/mailbox.py/_singlefileMailbox._lookup/original