13 useful tips about Python datetime objects

The Python datetime library provides several useful objects to manipulate times and dates. I’ve been using them a lot lately, and I want to share some useful operations that might be useful to you as well 😉

You can find a video version of this post at the bottom of the page 🙂

1. First, let’s import the datetime library and create three different kind of objects:
– date object: stores the date
– time object: stores the time
– datetime object: stores both the date and the time

If we create the datetime object first, we can extract its date and time and create the respective objects:

>>> import datetime
>>> now = datetime.datetime.now()
>>> today = now.date()
>>> moment = now.time()

If you print each of these items you’ll get something like:

>>> now
datetime.datetime(2014, 3, 23, 16, 38, 46, 271475)
>>> today
datetime.date(2014, 3, 23)
>>> moment
datetime.time(16, 38, 46, 271475)

Where you can see that the time is 16h 46min and 46.171475 seconds, and today is March 23rd, 2014.

2. You can also create a date and time objects and obtain a datetime object using the combine method:

>>> today = datetime.date.today()
>>> moment = datetime.datetime.now().time()
>>> now = datetime.datetime.combine(today, moment)

3. Another interesting object is the timedelta object, which can be used to sum or subtract a number of days:

>>> yesterday = today - datetime.timedelta(1)

Or it can store a datetime difference between two datetime objects:

>>> delta = yesterday - today

4. Date objects have three mandatory arguments (you can change its order by using keys):

>>> my_date = datetime.date(1984, 6, 24)
>>> my_date = datetime.date(day=24, year=1984, month=6)

5. Time objects don’t have mandatory arguments. These tree statements are equivalent:

>>> my_time = datetime.time() 
>>> my_time = datetime.time(0,0)  # first argument hour, second minute
>>> my_time = datetime.time(hour=0, minute=0)

6. Datetime objects have the same mandatory arguments as the date objects:

>>> my_datetime = datetime.datetime(year=1984, month=6, day=24)  # Time is set to 0:00
>>> my_other_datetime = datetime.datetime(1984, 6, 24, 18, 30) 
>>> my_other_datetime = datetime.datetime(year=1984, month=6, day=24, hour=18, minute=30)

7. Change one datetime object to obtain another using the replace method:

>>> another_datetime = my_datetime.replace(year=2014, month=1)

8. Obtain a datetime object representing the epoch: 01-01-1970:

>>> epoch = datetime.datetime.utcfromtimestamp(0)

9. Obtain the number of days and seconds between the epoch and now, or the total number of seconds that have passed:

>>> delta = now - epoch
>>> days = delta.days

>>> seconds = delta.seconds
>>> total_seconds = delta.total_seconds()

10. Recover now using the number of seconds since epoch using the utcfromtimestamp method:

>>> now = datetime.datetime.utcfromtimestamp(seconds)

11. Write a date object as “1984-06-24”:

>>> string_date = str(my_date)

12. Recover a date object from a string like “1984-06-24”:

>>> my_date = datetime.date(*[int(i) for i in string_date.split("-")])

13. Write a date object with a custom string format – the strftime method:

>>> string_date =  my_date.strftime('%m/%d/%Y')  # This writes "06/24/1984"

You can also check this video version made by Webucator. Don’t forget to visit their website to check their Python courses 🙂

Hope it’s useful! 🙂