Python: Effective way to convert ambiguous hours into time object?

Question

I have a list of strings as follows:

4:00-5:00PM
11:00-2:00PM
12:00-1:00PM
11:00-1:00AM

and I'm trying to find an effective way to create two time objects (I suppose this is the only way to keep track of a range of time, which I will later combine with a date object). It is clear to humans what we mean we say 11:00-1:00AM, but wondering what's an effective way to convert this to:

datetime.time(23, 0)
datetime.time(1, 0)

My current approach is to take the first time, and create a PM and AM version, take the timedelta with the end time (which is specified), and take the shorter of the two differences to be the correct one.

Answer 1

Here is a simple implementation.

    >>> def timeRange(timestr):
    ...     t1, t2 = timestr.split("-")
    ...     timeFormat = "%I:%M%p"
    ...     t1AM = datetime.datetime.strptime(t1 + "AM", timeFormat)
    ...     t1PM = datetime.datetime.strptime(t1 + "PM", timeFormat)
    ...     t2 = datetime.datetime.strptime(t2, timeFormat)
    ...       
    ...     if (t2 - t1AM).seconds < (t2-t1PM).seconds:
    ...         return t1AM.time(), t2.time()
    ...     else:
    ...         return t1PM.time(), t2.time()
    >>> timeRange("11:00-2:00PM")
    (datetime.time(11, 0), datetime.time(14, 0))
    >>> timeRange("4:00-5:00PM")
    (datetime.time(16, 0), datetime.time(17, 0))
    >>> timeRange("11:00-1:00AM")
    (datetime.time(23, 0), datetime.time(1, 0))
    >>> timeRange("11:00-2:00PM")
    (datetime.time(11, 0), datetime.time(14, 0))
    >>> timeRange("12:00-1:00PM")
    (datetime.time(12, 0), datetime.time(13, 0))

This returns a time object, but you could roll that into a datetime object if you need to.

Answer 2

There are two assumptions implicit in your question:

• You are looking for the shortest possible duration between these times
• The first time is the earlier of the two.

If these assumptions are true, then a quick optimization would be:

• If the first time is larger than the second (eg 11:00-1:00AM or 11:00-1:00PM) then the earlier time is the 'opposite' AM/PM indicator of the second. Otherwise, the AM/PM of the first time is the same.

This works even for the largest time period, eg 6:00-6:00AM (6:00PM-6:00AM is shorter than 6:00AM-6:00AM)

A second observation is that you cannot use the simple time object because

• An AM->PM duration takes place over a day boundary (midnight). This is probably screwing up the computation of your timedelta in this condition.

Therefore I think you have to use datetime, or wrap all this up in a structure that states the time in the first time object is the previous day.

Hope this helps :)