code: def set_user_preferences_from_request(request):
      
      prefs = []
  
      for pref in request.POST.getlist(_PREF_POST_KEY):
          message_alias, messenger_alias = pref.split(_ALIAS_SEP)
  
          try:
              get_registered_message_type(message_alias)
              get_registered_messenger_object(messenger_alias)
  
          except (UnknownMessengerError, UnknownMessageTypeError):
              pass
  
          else:
              prefs.append((message_alias, messenger_alias))
  
      Subscription.replace_for_user(request.user, prefs)
  
      return bool(prefs)
docs: Sets user subscription preferences using data from a request.
  
      Expects data sent by form built with `sitemessage_prefs_table` template tag.
  
      :param request:
      :rtype: bool
      :return: Flag, whether prefs were found in the request.