结束一天（日期时间）的最优雅的方式是什么？

我目前正在编写一些报告代码，允许用户选择指定日期范围。它的工作方式（简化）是：

• 用户（可选）指定年份。
• 用户（可选）指定月份。
• 用户（可选）指定一天。

这是一个代码片段，以及描述我想要的内容的注释like to do:

from datetime import datetime, timedelta

# ...

now = datetime.now()
start_time = now.replace(hour=0, minute=0, second=0, microsecond=0)
stop_time = now
# If the user enters no year, month, or day--then we'll simply run a
# report that only spans the current day (from the start of today to now).

if options['year']:
    start_time = start_time.replace(year=options['year'], month=0, day=0)
    stop_time = stop_time.replace(year=options['year'])
    # If the user specifies a year value, we should set stop_time to the last
    # day / minute / hour / second / microsecond of the year, that way we'll
    # only generate reports from the start of the specified year, to the end
    # of the specified year.

if options['month']:
    start_time = start_time.replace(month=options['month'], day=0)
    stop_time = stop_time.replace(month=options['month'])
    # If the user specifies a month value, then set stop_time to the last
    # day / minute / hour / second / microsecond of the specified month, that
    # way we'll only generate reports for the specified month.

if options['day']:
    start_time = start_time.replace(day=options['day'])
    stop_time = stop_time.replace(day=options['day'])
    # If the user specifies a day value, then set stop_time to the last moment of
    # the current day, so that reports ONLY run on the current day.

我正在尝试找到最优雅的方式来编写上面的代码——我一直在尝试找到一种使用 timedelta 来完成此操作的方法，但似乎无法弄清楚。任何意见，将不胜感激。

要设置stop_time， 进步start_time视情况而定的一年、一月或一天，然后减去一timedelta(microseconds=1)

if options['year']:
    start_time = start_time.replace(year=options['year'], month=1, day=1)
    stop_time = stop_time.replace(year=options['year']+1)-timedelta(microseconds=1)

elif options['month']:
    start_time = start_time.replace(month=options['month'], day=1)
    months=options['month']%12+1
    stop_time = stop_time.replace(month=months,day=1)-timedelta(microseconds=1)

else:
    start_time = start_time.replace(day=options['day'])
    stop_time = stop_time.replace(day=options['day'])+timedelta(days=1,microseconds=-1)