What is the standard way to add N seconds to datetime.time in Python?


Question

Given a datetime.time value in Python, is there a standard way to add an integer number of seconds to it, so that 11:34:59 + 3 = 11:35:02, for example?

These obvious ideas don't work:

>>> datetime.time(11, 34, 59) + 3
TypeError: unsupported operand type(s) for +: 'datetime.time' and 'int'
>>> datetime.time(11, 34, 59) + datetime.timedelta(0, 3)
TypeError: unsupported operand type(s) for +: 'datetime.time' and 'datetime.timedelta'
>>> datetime.time(11, 34, 59) + datetime.time(0, 0, 3)
TypeError: unsupported operand type(s) for +: 'datetime.time' and 'datetime.time'

In the end I have written functions like this:

def add_secs_to_time(timeval, secs_to_add):
    secs = timeval.hour * 3600 + timeval.minute * 60 + timeval.second
    secs += secs_to_add
    return datetime.time(secs // 3600, (secs % 3600) // 60, secs % 60)

I can't help thinking that I'm missing an easier way to do this though.

1
315
5/23/2017 11:47:26 AM

Accepted Answer

You can use full datetime variables with timedelta, and by providing a dummy date then using time to just get the time value.

For example:

import datetime
a = datetime.datetime(100,1,1,11,34,59)
b = a + datetime.timedelta(0,3) # days, seconds, then other fields.
print a.time()
print b.time()

results in the two values, three seconds apart:

11:34:59
11:35:02

You could also opt for the more readable

b = a + datetime.timedelta(seconds=3)

if you're so inclined.


If you're after a function that can do this, you can look into using addSecs below:

import datetime

def addSecs(tm, secs):
    fulldate = datetime.datetime(100, 1, 1, tm.hour, tm.minute, tm.second)
    fulldate = fulldate + datetime.timedelta(seconds=secs)
    return fulldate.time()

a = datetime.datetime.now().time()
b = addSecs(a, 300)
print a
print b

This outputs:

 09:11:55.775695
 09:16:55
445
1/15/2013 1:19:11 AM

As others here have stated, you can just use full datetime objects throughout:

sometime = get_some_time() # the time to which you want to add 3 seconds
later = (datetime.combine(date.today(), sometime) + timedelta(seconds=3)).time()

However, I think it's worth explaining why full datetime objects are required. Consider what would happen if I added 2 hours to 11pm. What's the correct behavior? An exception, because you can't have a time larger than 11:59pm? Should it wrap back around?

Different programmers will expect different things, so whichever result they picked would surprise a lot of people. Worse yet, programmers would write code that worked just fine when they tested it initially, and then have it break later by doing something unexpected. This is very bad, which is why you're not allowed to add timedelta objects to time objects.


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