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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 async def setLocalDescription(self, sessionDescription):
 """ Change the local description associated with the connection. :param: sessionDescription: An :class:`RTCSessionDescription` generated by :meth:`createOffer` or :meth:`createAnswer()`. """

        # parse and validate description
        description = sdp.SessionDescription.parse(sessionDescription.sdp)
        description.type = sessionDescription.type
        self.__validate_description(description, is_local=True)

        # update signaling state
        if description.type == 'offer':
            self.__setSignalingState('have-local-offer')
        elif description.type == 'answer':
            self.__setSignalingState('stable')

        # assign MID
        for i, media in enumerate(description.media):
            mid = media.rtp.muxId
            self.__seenMids.add(mid)
            if media.kind in ['audio', 'video']:
                transceiver = self.__getTransceiverByMLineIndex(i)
                transceiver._set_mid(mid)
            elif media.kind == 'application':
                self.__sctp.mid = mid

        # set ICE role
        if self.__initialOfferer is None:
            self.__initialOfferer = (description.type == 'offer')
            for iceTransport in self.__iceTransports:
                iceTransport._connection.ice_controlling = self.__initialOfferer

        # configure direction
        for t in self.__transceivers:
            if description.type in ['answer', 'pranswer']:
                t._currentDirection = and_direction(t.direction, t._offerDirection)

        # gather candidates
        await self.__gather()
        for i, media in enumerate(description.media):
            if media.kind in ['audio', 'video']:
                transceiver = self.__getTransceiverByMLineIndex(i)
                add_transport_description(media, transceiver._transport)
            elif media.kind == 'application':
                add_transport_description(media, self.__sctp.transport)

        # connect
        asyncio.ensure_future(self.__connect())

        # replace description
        if description.type == 'answer':
            self.__currentLocalDescription = description
            self.__pendingLocalDescription = None
        else:
            self.__pendingLocalDescription = description