def __init__(self, alert_expiry=1, alert_limit=100, **kwargs):
"""Return a new UserPolicy object.
Arguments:
alert_expiry -- The delay after a successful alert after which
the limit no longer applies.
alert_limit -- The number of alerts allowed.
"""
self.alert_expiry = alert_expiry
self.alert_limit = alert_limit
self._user = {}
for k, v in kwargs.iteritems():
if k not in self.allowed_attrs:
raise UnknownAttribute(attribute=k)
self._user[k] = v
if 'username' not in self._user:
raise MissingAttribute(attribute=username)