What is the difference between strftime and strptime?

strftime formats a datetime object into a string using directives like %Y. strptime parses a string back into a datetime using the same directives as the expected layout. The directive set is shared between them.

Why does %y differ from %Y?

%Y is the full four-digit year (2026), while %y is the zero-padded two-digit year (26). Use %Y in almost all cases; %y is ambiguous across centuries and mainly useful for compact legacy formats.

What does %j produce?

%j is the day of the year as a zero-padded three-digit number from 001 to 366. For example 1 January is 001 and 31 December in a leap year is 366. It is handy for ordinal date calculations.

Are weekday and month names locale-dependent?

Yes. %a, %A, %b, %B and %p depend on the active locale set with the locale module. By default Python uses the C locale, which produces English names. Set the LC_TIME locale to get localized output.

What is %Z versus %z?

%z is the UTC offset as a signed value like +0000 or -0530, while %Z is the time zone name such as UTC or BST. For naive datetimes both produce an empty string because no zone information is attached.

Python datetime Format Codes

Python’s datetime.strftime and datetime.strptime share one set of format directives, each beginning with %. Get one wrong and your parse silently fails or your output is off by a century. This tool is a searchable reference plus a live builder that renders any format string against a sample timestamp.

How it works

Each directive maps a part of a date or time to a piece of text. strftime walks your format string left to right and substitutes each %X with the corresponding field of the datetime; everything else is copied verbatim. strptime does the reverse, matching the input text against the directives.

The reference covers the standard C89 directives that CPython supports on every platform — year (%Y, %y), month (%m, %b, %B), day (%d, %j), weekday (%a, %A, %w, %u), time (%H, %I, %M, %S, %p), microseconds (%f), zone (%z, %Z), week numbers (%U, %W, %V, %G), and the locale shortcuts (%c, %x, %X). A literal percent sign is %%.

Worked example

For the timestamp 2026-06-11 14:05:09:

%Y-%m-%d        -> 2026-06-11
%d/%m/%Y        -> 11/06/2026
%A, %d %B %Y    -> Thursday, 11 June 2026
%I:%M %p        -> 02:05 PM
%j (day of yr)  -> 162

The builder above renders your own string the same way so you can confirm the layout before pasting it into code.

Notes

Zero-padding is the default for numeric directives. Platform extensions like %-d (no leading zero) exist on Linux and macOS but are not portable to Windows, so this reference treats them as non-standard.
%f always produces six digits (microseconds), padded with zeros.
ISO week directives %G, %V, %u form a consistent ISO 8601 triple and should be used together, never mixed with %Y, %U, or %W.
Names produced by %a, %A, %b, %B, and %p follow the active locale.

Python datetime Format Codes

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How it works

Worked example

Notes