class UserNotFoundError(Exception):
    def __init__(self):
        super().__init__('user not found')


class GroupNotFoundError(Exception):
    def __init__(self):
        super().__init__('group not found')


class BadRequest(Exception):
    pass


class KerberosError(Exception):
    pass


class UserAlreadyExistsError(Exception):
    def __init__(self):
        super().__init__('user already exists')


class GroupAlreadyExistsError(Exception):
    def __init__(self):
        super().__init__('group already exists')


class UserAlreadySubscribedError(Exception):
    def __init__(self):
        super().__init__('user is already subscribed')


class UserNotSubscribedError(Exception):
    def __init__(self):
        super().__init__('user is not subscribed')


class NoSuchListError(Exception):
    def __init__(self):
        super().__init__('mailing list does not exist')