def listen(description, factory):
    """
    Listen on a port corresponding to a description.

    @param description: The description of the connecting port, in the syntax
        described by L{twisted.internet.endpoints.serverFromString}.
    @type description: L{str}

    @param factory: The protocol factory which will build protocols on
        connection.
    @type factory: L{twisted.internet.interfaces.IProtocolFactory}

    @rtype: L{twisted.internet.interfaces.IListeningPort}
    @return: the port corresponding to a description of a reliable virtual
        circuit server.

    @see: L{twisted.internet.endpoints.serverFromString}
    """
    from twisted.internet import reactor
    name, args, kw = endpoints._parseServer(description, factory)
    return getattr(reactor, 'listen' + name)(*args, **kw)

    Listen on a port corresponding to a description.

    @param description: The description of the connecting port, in the syntax
        described by L{twisted.internet.endpoints.serverFromString}.
    @type description: L{str}

    @param factory: The protocol factory which will build protocols on
        connection.
    @type factory: L{twisted.internet.interfaces.IProtocolFactory}

    @rtype: L{twisted.internet.interfaces.IListeningPort}
    @return: the port corresponding to a description of a reliable virtual
        circuit server.

    @see: L{twisted.internet.endpoints.serverFromString}
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/strports.py