gh-41431: Add datetime.time.strptime() and datetime.date.strptime()

[nineteendo]

• Issue: Add datetime.time.strptime and datetime.date.strptime #41431

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📚 Documentation preview 📚: library/datetime.html

[nineteendo]

Is it fine to have this note twice in the documentation?

[pganssle]

I think documentation experts will know better than me, but I think there's a way to define a substitution for this, like this:

|format-note|

.. |format-note| replace::
    If *format* specifies a day of month without a year a :exc:`DeprecationWarning` is emitted. This is to avoid a quadrenial leap year bug in code seeking to parse only a month and day, as the default year used when unspecified in the format is not a leap year. Such *format* values may raise an error in Python 3.15. The workaround is to always include a year in your *format*. If parsing *date_string* values that do not have a year, explicitly add a year that is a leap year before parsing:
    .. doctest::
        
        >> from datetime import date
        >> date_string = "02/29"
        >> when = date.strptime(f"{date_string};1984", "%m/%d;%Y")  # Avoids leap year bug.
        >> when.strftime("%B %d") # doctest: +SKIP
        'February 29'

.. versionadded:: 3.14

Then you put |format-note| in the other place as well.

Two other options:

1. move this to a small fragment file (seems like overkill), and use an ..include directive with it.
2. put the note in one place, then link to it in the other place (e.g. "See the note on :func:datetime.strptime").

I don't think there's a simple way to do it with a parameter, though.

[nineteendo]

I was just wondering if it was a problem it was mentioned twice. Do I link to datetime.strptime or is this fine?

[vstinner]

@vstinner, would you like to review this? (You requested changes on the old pull request)

I skip my turn :-)

[picnixz]

So I had a pending review that I forgot to send. Here are some comments!

[pganssle]

This looks great so far! I have some suggestions here mostly about the tests.

I'm also working on some hypothesis based tests for this, because there are a couple of properties that we can easily and usefully test here, specifically:

1. dt == dt.strptime(dt.strftime(format), format) == dt
2. my_datetime.strftime(format_with_just_dates).date() == my_datetime.date().strftime(format_with_just_dates)
3. my_datetime.strftime(format_with_just_times).time() == my_datetime.time().strftime(format_with_just_times)

I think the key will just be getting a good hypothesis strategy that generates the format strings.

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[pganssle]

Awesome, looks good to me! Glad to finally have this done!

[pganssle]

Thanks @nineteendo! Really great work on this one. Thanks for your patience waiting for reviews and your quick response when the reviews came!

[nineteendo]

Can you close the issue?