docs: def latlng(arg):
      """Converts a lat/lon pair to a comma-separated string.
  
      For example:
  
      sydney = {
          "lat" : -33.8674869,
          "lng" : 151.2069902
      }
  
      convert.latlng(sydney)
      # '-33.8674869,151.2069902'
  
      For convenience, also accepts lat/lon pair as a string, in
      which case it's returned unchanged.
  
      :param arg: The lat/lon pair.
      :type arg: string or dict or list or tuple
      """
      if is_string(arg):
          return arg
  
      normalized = normalize_lat_lng(arg)
      return "%s,%s" % (format_float(normalized[0]), format_float(normalized[1]))