How to add two datetime.datetime objects?

Question

I want to add two datetime objects.

>>> from datetime import datetime
>>> a = datetime.strptime("04:30",'%H:%M')
>>> b = datetime.strptime("02:30",'%H:%M')
>>> a
datetime.datetime(1900, 1, 1, 4, 30)
>>> b
datetime.datetime(1900, 1, 1, 2, 30)

when i subtract b from a, it gives me the output

>>> a-b
datetime.timedelta(0, 7200)

but, when i add a and b it gives me error

>>> a+b
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
 TypeError: unsupported operand type(s) for +: 'datetime.datetime' and    'datetime.datetime'

I want to add the time of b to time of a, i.e i want this.

datetime.datetime(1900, 1, 1, 7, 00)

please help ?

Adding dates does not make sense. There is no logical reason to expect the output you want (why should the hours and minutes be added but not the years, months and days?) — jonrsharpe
– jonrsharpe, Commented Mar 11, 2015 at 13:47
While adding dates does not make sense, what you want is probably to add a time difference to a time. Therefore, you should make your b not a datetime object, but a timedelta object. — physicalattraction
– physicalattraction, Commented Mar 11, 2015 at 13:50

mattvivier · Accepted Answer · 2015-03-11 14:38:10Z

7

Agreeing with the previous poster, there isn't a meaningful way to add two datetimes, as they're just points in time, you can only deal with the difference between them (timedeltas). Since you don't explicitly mention the dates in your example, this seems like it would be more along the lines of what you're trying to accomplish:

>>> a = datetime.timedelta(0, (4*3600+30*60))
>>> b = datetime.timedelta(0, (2*3600+30*60))
>>> a+b
datetime.timedelta(0, 25200)
>>> print a+b
7:00:00

As timedeltas take days, seconds, and microseconds you need to multiply your hours and minutes to get them to the correct base.

answered Mar 11, 2015 at 14:38

mattvivier

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Comments

Mike D Sutton · Accepted Answer · 2023-08-04 09:56:45Z

1

We recently came across a similar scenario where we were provide two datetime values, one containing just a date (but no time) and another containing just a time.

Here's the solution we ended up with in case it helps anyone else in future:

from datetime import datetime, timedelta

BASE_DATE = datetime(1900, 1, 1)

def sumDateTimes(dates):
    return sum((dt - BASE_DATE for dt in dates), timedelta(0)) + BASE_DATE

Example:

a = datetime.strptime("1-Aug-23", "%d-%b-%y")
b = datetime.strptime("10 AM", "%I %p")
print(sumDateTimes([ a, b ]))
>>> 2023-08-01 10:00:00

answered Aug 4, 2023 at 9:56

Mike D Sutton

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2 Comments

slothrop Over a year ago

datetime.combine is the most natural way of solving this requirement: docs.python.org/3/library/…. Specifically: print(datetime.combine(a, b.time())) will give the required "2023-08-01 10:00:00".

Mike D Sutton Over a year ago

@slothrop datetime.combine would work for this particular scenario, however the above would work regardless of which order the dates were specified and would additionally handle multiple time offsets or even offsets of larger than a day.

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