如何获得从PM到AM的开始时间和结束时间之间的时间差？

import datetime

def calculate_time_difference(pm_start, pm_end, am_start, am_end):
    # 将开始时间和结束时间转换为datetime对象
    pm_start_time = datetime.datetime.strptime(pm_start, '%H:%M')
    pm_end_time = datetime.datetime.strptime(pm_end, '%H:%M')
    am_start_time = datetime.datetime.strptime(am_start, '%H:%M')
    am_end_time = datetime.datetime.strptime(am_end, '%H:%M')

    # 计算开始时间和结束时间的时间差
    time_difference = (am_start_time - pm_end_time) + (am_end_time - am_start_time)

    # 格式化时间差为小时:分钟:秒的形式
    formatted_difference = str(time_difference)

    return formatted_difference

# 示例使用
pm_start_time = '10:00'
pm_end_time = '12:30'
am_start_time = '13:30'
am_end_time = '15:00'

time_difference = calculate_time_difference(pm_start_time, pm_end_time, am_start_time, am_end_time)
print("从PM到AM的时间差为:", time_difference)