code: def time_zones_for_number(numobj):
      
      ntype = number_type(numobj)
      if ntype == PhoneNumberType.UNKNOWN:
          return _UNKNOWN_TIME_ZONE_LIST
      elif not is_number_type_geographical(ntype, numobj.country_code):
          return _country_level_time_zones_for_number(numobj)
      return time_zones_for_geographical_number(numobj)
docs: As time_zones_for_geographical_number() but explicitly checks the
      validity of the number passed in.
  
      Arguments:
      numobj -- a valid phone number for which we want to get the time zones to which it belongs
      Returns a list of the corresponding time zones or a single element list with the default
      unknown time zone if no other time zone was found or if the number was invalid