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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:
 def _CreateRoutePatternsFolder(self, parent, route, style_id=None, visible=True):
 """Create a KML Folder containing placemarks for each pattern in the route. A pattern is a sequence of stops used by one of the trips in the route. If there are not patterns for the route then no folder is created and None is returned. Args: parent: The parent ElementTree.Element instance. route: The transitfeed.Route instance. style_id: The id of a style to use if not None. visible: Whether the folder is initially visible or not. Returns: The Folder ElementTree.Element instance or None if there are no patterns. """

    pattern_id_to_trips = route.GetPatternIdTripDict()
    if not pattern_id_to_trips:
      return None

    # sort by number of trips using the pattern
    pattern_trips = pattern_id_to_trips.values()
    pattern_trips.sort(lambda a, b: cmp(len(b), len(a)))

    folder = self._CreateFolder(parent, 'Patterns', visible)
    for n, trips in enumerate(pattern_trips):
      trip_ids = [trip.trip_id for trip in trips]
      name = 'Pattern %d (trips: %d)' % (n+1, len(trips))
      description = 'Trips using this pattern (%d in total): %s' % (
          len(trips), ', '.join(trip_ids))
      placemark = self._CreatePlacemark(folder, name, style_id, visible,
                                        description)
      coordinates = [(stop.stop_lon, stop.stop_lat)
                     for stop in trips[0].GetPattern()]
      self._CreateLineString(placemark, coordinates)
    return folder