def _validate_quota(quota):
    '''
    Helper to verify that quota parameters are valid
    '''
    if quota is not None:
        if not isinstance(quota, dict):
            raise TypeError('quota must be a dictionary, provided value: {0}'.format(quota))
        periods = ['DAY', 'WEEK', 'MONTH']
        if 'period' not in quota or quota['period'] not in periods:
            raise ValueError('quota must have a valid period specified, valid values are {0}'.format(','.join(periods)))
        if 'limit' not in quota:
            raise ValueError('quota limit must have a valid value')
Helper to verify that quota parameters are valid