old_contents: import attr
  
  
  @attr.s
  class RTCTrackEvent:
      """
      This event is fired on :class:`RTCPeerConnection` when a new
      :class:`MediaStreamTrack` is added by the remote party.
      """
      receiver = attr.ib()  # type: RTCRtpReceiver
      "The :class:`RTCRtpReceiver` associated with the event."
      track = attr.ib()  # type: MediaStreamTrack
      "The :class:`MediaStreamTrack` associated with the event."
      transceiver = attr.ib()  # type: RTCRtpTransceiver
      "The :class:`RTCRtpTransceiver` associated with the event."
  
new_contents: import attr
  
  from .mediastreams import MediaStreamTrack
  from .rtcrtpreceiver import RTCRtpReceiver
  from .rtcrtptransceiver import RTCRtpTransceiver
  
  
  @attr.s
  class RTCTrackEvent:
      """
      This event is fired on :class:`RTCPeerConnection` when a new
      :class:`MediaStreamTrack` is added by the remote party.
      """
      receiver = attr.ib()  # type: RTCRtpReceiver
      "The :class:`RTCRtpReceiver` associated with the event."
      track = attr.ib()  # type: MediaStreamTrack
      "The :class:`MediaStreamTrack` associated with the event."
      transceiver = attr.ib()  # type: RTCRtpTransceiver
      "The :class:`RTCRtpTransceiver` associated with the event."
  
subject: fix PEP8 error