Python: Formatting dates and times

Formatting dates and times into human-readable strings is a common programming task, and Python has a comprehensive method for doing so.

Let's begin by importing the datetime and tz (timezone) libraries:

>>> import datetime
>>> from dateutil import tz

The datetime library has many useful (and advanced) classes and methods, but exploring them is beyond the scope of this article. To explore formatting dates and times in Python, we will begin by generating a specific datetime, far out in the future. This will provide us with uniquely recognizable string components in our examples below.

Python datetime objects contain the following information, in order: Year, Month, Day, Hour, Minute, Second, Millisecond, and Timezone. Let's generate the datetime for May 4, 9876, at exactly 1.001 seconds after 3:02AM, in Los Angeles. :

>>> location = tz.gettz('America/Los_Angeles')
>>> dt = datetime.datetime(9876, 5, 4, 3, 2, 1, 1, tzinfo=location)

To format our datetime, we use its strftime() method. Let's try a few examples.

Dates

Let's format our date per the ISO 8601 standard, which is my personal favorite and takes the form "YYYY-MM-DD":

>>> dt.strftime("%Y-%m-%d")
'9876-05-04'

You may notice that the formatting is controlled by characters preceded with a %. These are called "directives", and allow us to declare formatting for specific parts of the date and time, while mixing in other plaintext characters, like -. There is a reference chart of most strftime() directives at the end of this article.

Let's try another. In many parts of the world, it's common to format dates as "DD.MM.YY":

>>> dt.strftime("%d.%m.%y")
'04.05.76'

(You may notice that the lowercase y directive yields a two-character year, instead of the four-character year yielded by the uppercase Y directive.)

Finally, let's try a format like "Weekday Name, Month Name (Abbreviated) Date, Year":

>>> dt.strftime("%A, %b %d, %Y")
'Thursday, May 04, 9876'

Times

Now we'll format the time.

First, let's try 24-hour time, like "HH:MM:SS":

>>> dt.strftime("%H:%M:%S")
'03:02:01'

And let's also do 12-hour time, without seconds, showing whether it's AM or PM:

>>> dt.strftime("%-I:%M%p")
'3:02AM'

Directives

By mixing and matching the directives below, we can now freely format dates and times in Python:

(NOTE: Python implements strftime() by calling strftime() in the platform's C library. Not all directives are available on all platforms, and some platforms may have directives not shown here. These directives were tested in Python 3.8 on macOS 10.15.4.)

Dates

Times

Short Codes

Misc

Documentation for strftime().

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