def _lookup(self, key):
        """Use TOC to return subpath for given key, or raise a KeyError."""
        try:
            if os.path.exists(os.path.join(self._path, self._toc[key])):
                return self._toc[key]
        except KeyError:
            pass
        self._refresh()
        try:
            return self._toc[key]
        except KeyError:
            raise KeyError('No message with key: %s' + key)

    # This method is for backward compatibility only.
dataset/ETHPy150Open babble/babble/include/jython/Lib/mailbox.py/Maildir._lookup/operator `%` -> `+`