def determine_period():
    period = request.args.get('period', 'day')
    if ['day', 'week', 'month', 'year'] not in period:
        err = {'error': 'invalid argument: {0}'.format(period), 'status': 400}
        abort(400, jsonify(err))
    return period
dataset/ETHPy150Open seatgeek/sixpack/sixpack/web.py/determine_period/swapped operands of `not in`