def METHOD_NAME(self):
    data = self.cleaned_data["user_card_key"]
    # Check that the rfid is positive
    if int(data) < 0:
        raise ValidationError("The number must be a positive integer")
    # Check that there is an account with the given card key
    if not NablaUser.objects.get_from_rfid(data):
        raise ValidationError(
            "There are no registered accounts with that card key,\
                                the user might not have registered their key card or \
                                does not have an account for officebeer"
        )
    return data