'Send an event recording an experiment bucketing.
experiment_id: an integer representing the experiment
experiment_name: a human-readable name representing the experiment
variant: a string representing the variant name
user: the Account that has been put into the variant'

def bucketing_event(self, experiment_id, experiment_name, variant, user, loid):

    event = Event(topic='bucketing_events', event_type='bucket')
    event.add('experiment_id', experiment_id)
    event.add('experiment_name', experiment_name)
    event.add('variant', variant)
    if (user is not None):
        event.add('user_id', user._id)
        event.add('user_name', user.name)
    if loid:
        for (k, v) in loid.to_dict().iteritems():
            event.add(k, v)
    self.save_event(event)
