def getModificationTime(self, key):
        """
        Returns modification time of an entry.

        @return: Last modification date (seconds since epoch) of entry C{key}
        @raise KeyError: Raised when there is no such key
        """
        if not type(key) == bytes:
            raise TypeError("DirDBM key must be bytes")
        path = self._dnamePath.child(self._encode(key))
        if path.isfile():
            return path.getModificationTime()
        else:
            raise KeyError(key)

        Returns modification time of an entry.

        @return: Last modification date (seconds since epoch) of entry C{key}
        @raise KeyError: Raised when there is no such key
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/persisted/dirdbm.py