Getting To Grips With Python Dates

I don't know if its because I picked up PHP first, but learning to work with dates in Python has been an uphill battle. Something as trivial as converting a string to a date object can seem convoluted if you don't know where to start. I wrote this post in an attempt to address some of these common questions.

Convert A String To A Datetime Object


This one is pretty easy, but I still see it asked all over the place. You want to convert a string such as 2012-04-25 to a datetime object. Here's how its done:

from datetime import date time

my_date_string = '2012-04-25'
my_date_object = datetime.strptime(my_date_string, '%Y-%m-%d')

The meat and potatos of this is the strptime function. The first argument is the string, and the second is the format that string is in. The function uses that format to parse your string and create the date object. Simple.

Convert A Datetime Object To A Formatted String


This is basically the opposite of the previous example. You want to take a datetime object, say from a document record returned by MongoDB, and output it as a nicely formatted string.

from datetime import date time

my_date_object = datetime.utcnow()
my_date_string = my_date_object.strftime('%Y-%m-%d')

The above example will get the current UTC date as a datetime object, then use that objects strftime method to return a string in the format specified. You can find information on the supported format codes in the Python docs.

Convert A Datetime Object To A Unix Timestamp


Converting a datetime object to a Unix timestamp is a common step when working with localized dates or when making a public API where you want a standard date format supported by many other languages. Here's how to do it.

import time
from datetime import date time

my_date_object = datetime.utcnow()
unix_timestamp = time.mktime(my_date_object.timetuple())

Here we're using the datetime objects timetuple method to create the argument list required by the mktime function. The result is our datetime object as a Unix timestamp. Bam!

Convert A Unix Timestamp To A Datetime Object


Naturally, the question after reading the above example would be: "How do I convert a Unix timestamp back to a Datetime object?".

Thats as easy as pie, check it out:

from datetime import date time

my_date_object = datetime.fromtimestamp(unix_timestamp)

Borrowing the unix_timestamp variable from the previous example, we're simply passing it as an argument to the fromtimestamp function. The result is our Unix timestamp converted back to a Python datetime object. Hooray!

Adding "st", "nd" and "rd" to Formatted Dates


This was a question that had me scratching my head for a while. Something that was so easy for me in PHP, wasn't possible with the default format codes in Python. Luckly, I came across a simple function that produces the same result. It's not as clean as using a format code, but it gets the job done.

from datetime import datetime as dt

def suffix(d):
    return 'th' if 11<=d<=13 else {1:'st',2:'nd',3:'rd'}.get(d%10, 'th')

def custom_strftime(format, t):
    return t.strftime(format).replace('{S}', str(t.day) + suffix(t.day))

print custom_strftime('%B {S}, %Y', dt.now())

This snippet was taken from an example on Stackoverflow. I'd recommend checking it out to see some of the other approaches and usage details.


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