docs: def activation_key_expired(self):
          """
          Checks if activation key is expired.
  
          Returns ``True`` when the ``activation_key`` of the user is expired 
          and ``False`` if the key is still valid.
  
          The key is expired when it's set to the value defined in
          ``ACCOUNTS_ACTIVATED`` or ``activation_key_created`` is beyond the
          amount of days defined in ``ACCOUNTS_ACTIVATION_DAYS``.
  
          """
          expiration_days = datetime.timedelta(
                              days=defaults.ACCOUNTS_ACTIVATION_DAYS)
          expiration_date = self.date_joined + expiration_days
          if self.activation_key == defaults.ACCOUNTS_ACTIVATED:
              return True
          if get_datetime_now() >= expiration_date:
              return True
          return False