def lookupChannel(channelType, windowSize, maxPacket, data):
        """
        The other side requested a channel of some sort.

        C{channelType} is the type of channel being requested,
        as an ssh connection protocol channel type.
        C{data} is any other packet data (often nothing).

        We return a subclass of L{SSHChannel<ssh.channel.SSHChannel>}.  If
        the channel type is unknown, we return C{None}.

        For other failures, we raise an exception. If a
        L{ConchError<error.ConchError>} is raised, the C{.value} will
        be the message, and the C{.data} will be the error code.

        @param channelType: The requested channel type
        @type channelType:  L{bytes}
        @param windowSize:  The initial size of the remote window
        @type windowSize:   L{int}
        @param maxPacket:   The largest packet we should send
        @type maxPacket:    L{int}
        @param data:        Additional request data
        @type data:         L{bytes}
        @rtype:             a subclass of L{SSHChannel} or L{None}
        """

        The other side requested a channel of some sort.

        C{channelType} is the type of channel being requested,
        as an ssh connection protocol channel type.
        C{data} is any other packet data (often nothing).

        We return a subclass of L{SSHChannel<ssh.channel.SSHChannel>}.  If
        the channel type is unknown, we return C{None}.

        For other failures, we raise an exception. If a
        L{ConchError<error.ConchError>} is raised, the C{.value} will
        be the message, and the C{.data} will be the error code.

        @param channelType: The requested channel type
        @type channelType:  L{bytes}
        @param windowSize:  The initial size of the remote window
        @type windowSize:   L{int}
        @param maxPacket:   The largest packet we should send
        @type maxPacket:    L{int}
        @param data:        Additional request data
        @type data:         L{bytes}
        @rtype:             a subclass of L{SSHChannel} or L{None}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/interfaces.py