class InvalidAmountError(ValueError):
    '''Raise when some member is already registered'''

class AlreadyRegisteredError(Exception):
    '''Raise when some member is already registered'''

class NotRegisteredError(Exception):
    '''Raise when the sender is not registered'''

class InvalidArgumentError(Exception):
    '''Raise when some cmd is called with wrong arguments'''

class NotAllowedError(Exception):
    '''Raise when some member is already registered'''