code: def get_or_add_media_part(self, media):
          
          media_part = self._find_by_sha1(media.sha1)
          if media_part is None:
              media_part = MediaPart.new(self._package, media)
          return media_part
docs: Return a |MediaPart| object containing the media in *media*.
  
          If this package already contains a media part for the same
          bytestream, that instance is returned, otherwise a new media part is
          created.