def connectionLost(reason):
        """
        The underlying connection has been lost.

        @param reason: A failure instance indicating the reason why
            the connection was lost.
        @type reason: L{twisted.python.failure.Failure}
        """

        The underlying connection has been lost.

        @param reason: A failure instance indicating the reason why
            the connection was lost.
        @type reason: L{twisted.python.failure.Failure}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/http.py