old_contents: from django.utils.text import mark_safe
  
  CASCADE_PLUGINS = ['map']
  
  def set_defaults(config):
      config.setdefault('leaflet', {})
      config['leaflet'].setdefault('tilesURL', 'http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png'),
      config['leaflet'].setdefault('default_position', {'lat': 30.0, 'lng': -40.0, 'zoom': 3})
      config['leaflet'].setdefault('id', 'mapbox.streets'),
      config['leaflet'].setdefault('maxZoom', 18),
      config['leaflet'].setdefault('detectRetina', True)
      config['leaflet'].setdefault('attribution', mark_safe('Map data &copy; <a href="http://openstreetmap.org">OpenStreetMap</a>')),
  
new_contents: from django import VERSION as DJANGO_VERSION
  if DJANGO_VERSION < (2, 0):
      from django.utils.text import mark_safe
  else:
  from django.utils.safestring import mark_safe
  
  CASCADE_PLUGINS = ['map']
  
  def set_defaults(config):
      config.setdefault('leaflet', {})
      config['leaflet'].setdefault('tilesURL', 'http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png'),
      config['leaflet'].setdefault('default_position', {'lat': 30.0, 'lng': -40.0, 'zoom': 3})
      config['leaflet'].setdefault('id', 'mapbox.streets'),
      config['leaflet'].setdefault('maxZoom', 18),
      config['leaflet'].setdefault('detectRetina', True)
      config['leaflet'].setdefault('attribution', mark_safe('Map data &copy; <a href="http://openstreetmap.org">OpenStreetMap</a>')),
  
subject: Update settings.py