gh-148823: Avoid importing _colorize when creating an ArgumentParser

[DavidCEllis]

This is one approach to deferring the _colorize import further.

This makes ._theme and ._decolor into properties so that _colorize is no longer imported when _set_color is called, but only when the theme is accessed.

Currently to prevent the import from subsequently being triggered when a subparser is created, this adds a 'fake' _colorless_theme which just returns empty strings for all attributes which replaces the actual colourless theme from _colorize.

Effectively this is what the colourless theme from _colorize does. I wanted to avoid duplicating all of the attribute names here or further complicating the logic, but there may be a better way to handle this.

Testing this did require an addition to the ensure_lazy_imports test helper to allow running additional code before checking for lazy imports. I think this might also be useful elsewhere when testing imports aren't being triggered earlier than intended.

Command: ./python -c 'import argparse; argparse.ArgumentParser()'

Benchmark 1: main
Time (mean ± σ): 28.7 ms ± 3.3 ms [User: 24.1 ms, System: 4.3 ms]
Range (min … max): 22.2 ms … 46.4 ms 200 runs
Benchmark 2: lazy colorize
Time (mean ± σ): 21.6 ms ± 5.8 ms [User: 17.3 ms, System: 4.0 ms]
Range (min … max): 12.1 ms … 36.0 ms 200 runs
Summary
lazy colorize ran
1.33 ± 0.39 times faster than main

Note that this uses the new lazy imports, this would need significant tweaking if it were to be backported to 3.14.

• Issue: argparse in 3.14+ is importing _colorize earlier than necessary #148823

[DavidCEllis]

Ah this pinged more people than I had anticipated.

This appears to be due to the modification to import_helper.py to allow for testing lazy imports with additional logic.

[JelleZijlstra]

Is it worth also checking .parse_args()? I think a good outcome is we only import colorize in the uncommon case where there's a parsing error or we invoke --help.

[DavidCEllis]

Yes, it probably is. I'll add one. I'm fairly sure I at least tried this...

[read-the-docs-community]

Documentation build overview

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[JelleZijlstra]

This mostly looks good and I'd like to get it into 3.15, but tests are failing, we're actually still importing _colorize in one of the paths.

[DavidCEllis]

Yes, locally on this branch I'm not though which is a little confusing... All of the lazy import tests are now failing. I assume I'll have to handle the merge conflicts to figure out what's going on?

[JelleZijlstra]

Inline comments seem to disappear, but wanted to add that it would be nice to make it so parsing args doesn't trigger the lazy import of shutil. It's apparently only used in the HelpFormatter, which intuitively we shouldn't need if we're not showing help. However, that may be a more involved change than we can get in for 3.15.

[DavidCEllis]

The shutil usage can probably be replaced - it's an environment variable check and then a call to os.get_terminal_size

[JelleZijlstra]

I feel ideally we should avoid instantiating the HelpFormatter at all but haven't looked into how hard that is. Having to inline get_terminal_size() would be a bit unfortunate.

[DavidCEllis]

Ah, it's #149375

[DavidCEllis]

I generally agree on avoiding the HelpFormatter, there seems to be a lot of logic that gets formatted fairly early though.

[savannahostrowski]

Overall, this looks great!

The only thing that we may want to consider is that since _colorize is private and _ColorlessTheme exists as an unenforced parallel implementation of ThemeSection.no_colors(), it may be worth adding a small test that imports _colorize, grabs get_theme(force_no_color=True).argparse, iterates its fields, and asserts each is ""?

[DavidCEllis]

Overall, this looks great!

The only thing that we may want to consider is that since _colorize is private and _ColorlessTheme exists as an unenforced parallel implementation of ThemeSection.no_colors(), it may be worth adding a small test that imports _colorize, grabs get_theme(force_no_color=True).argparse, iterates its fields, and asserts each is ""?

That's fine, I can do that.

I'm just trying to work out how to stop the import from being triggered due to the changes from #149375

Right now when any argument is added the help check now calls _apply_text_markup on the help string, importing _colorize due to this change https://github.com/DavidCEllis/cpython/blame/43b1c51105944aea17623e47f45294ba6b571c0c/Lib/argparse.py#L714

[savannahostrowski]

I cannot believe I have to comment via screenshot but inline comments don't work so...

I think this should be safe to do since it's read only anyway?

[DavidCEllis]

Yes! That's what I was looking for. I had got around to turning it off just for _check_help but this is better.

Edit: Now how do I accept a change from a screenshot 😆

[savannahostrowski]

Edit: Now how do I accept a change from a screenshot 😆

GitHub employees, if you're listening, I have a Copilot feature request.

[savannahostrowski]

LGTM! Thank you!