假设你获取了用户输入的日期和时间如2015-1-21 9:01:30，以及一个时区信息如UTC+5:00，均是str，请编写一个函数将其转换为timestamp

import re
from datetime import datetime,timedelta,timezone

def to_timestamp(dt_str, tz_str):
    cday = datetime.strptime(dt_str,'%Y-%m-%d %H:%M:%S')#字符串转为时间
    utc_group = re.match(r'([UTC]+)([+-])(\d+):(\d)',tz_str)#字符串匹配，分组
    i = int(utc_group.group(3))#时区数字
    if utc_group.group(2) == '+':#时区正负号
        tz_utc = timezone(timedelta(hours=i))
    elif utc_group.group(2) == '-':
        tz_utc = timezone(timedelta(hours=-i))
    dt = cday.replace(tzinfo=tz_utc)#给tzinfo属性赋值
    return dt.timestamp()

#测试
t1 = to_timestamp('2015-6-1 08:10:30', 'UTC+7:00')
assert t1 == 1433121030.0, t1

t2 = to_timestamp('2015-5-31 16:10:30', 'UTC-09:00')
assert t2 == 1433121030.0, t2

print('ok')

题目来源：廖雪峰老师的python教程-常用内建模块-datetime