gh-144384: Lazily import _colorize

[hugovk]

Lazily import _colorize to avoid slow construction/import when not needed.

The easily testable:

Before	After
difflib: 10ms	2ms (80% faster)
doctest: 48ms	40ms (17% faster)
json.tool: 13ms	6ms (54% faster)
pdb: 43ms	37ms (14% faster)
traceback: 15ms	8ms (47% faster)
unittest: 20ms	14ms (30% faster)

Some indirect improvements:

Before	After
asyncio: 47ms	27ms (43% faster)
logging: 17ms	10ms (41% faster)

traceback needs some extra handling: add a shutdown theme, so if it attempts to reify _colorize during shutdown when the import machinery is no longer around, it has a no-op fallback.

Also add ensure_lazy_imports tests.

• Issue: _colorize module is slow to import, affecting traceback and logging modules #144384

[picnixz]

Can we have a convention for lazy imports

[hugovk]

Can we have a convention for lazy imports

Yes, given we don't have a convention, and the SC left it the details to linters and auto-formatters, let's generally follow the Ruff/isort convention:

importjsonimportosimportsubprocessfromcollectionsimportdefaultdictfrompathlibimportPathfromtypingimportFinallazyimportastlazyimportshutillazyfromdataclassesimportdataclass

• astral-sh/ruff#23762
• astral-sh/ruff#21305
• PyCQA/isort#2503
• PyCQA/isort#2462

[StanFromIreland]

Seeing #149321, I think this should wait till that is somewhat figured out.

[hugovk]

Seeing #149321, I think this should wait till that is somewhat figured out.

#149338 has been merged, updating.

[hugovk]

And both the commands from #149321 are working.

---

The CIFuzz failures are unrelated network errors:

413.7 E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/universe/t/tcltk-defaults/tcl-dev_8.6.9+1_amd64.deb Connection failed [IP: 185.125.190.81 80]

There's another outage: https://status.canonical.com/#/incident/KNms6QK9ewuzz-7xUsPsNylV20jEt5kyKsd8A-3ptQG1OfBTMZO_fBkVMmGqQC3NLBLamiI6KOEL7KpsobFJ4Q==

[hugovk]

CIFuzz now also passing.

[sergey-miryanov]

Looks good to me, but I'm not very familiar with lazy imports.

[JelleZijlstra]

I'm not sure this makes sense for the pyrepl modules. Aren't those essentially always going to want _colorize?

[DavidCEllis]

I'm not sure the sqlite.__main__ lazy import is worthwhile? While it's not imported at top level, main will immediately import it with ArgumentParser() or get_theme a little later.

[hugovk]

I'm not sure this makes sense for the pyrepl modules. Aren't those essentially always going to want _colorize?

NO_COLOR=1 ./python.exe is a thing, and gives you a colour-free REPL.

But it still gets imported:

❯ NO_COLOR=1 ./python.exe
Python 3.15.0a8+ (heads/3.15-lazy-_colorize:2d346d5a1ea, May 6 2026, 16:40:10) [Clang 17.0.0 (clang-1700.6.4.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> "_colorize" in sys.modules
True

So I'll remove that change.

[hugovk]

And reverted in sqlite3.__main__ as well.

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #32566767 | 📁 Comparing ed1f8e6 against main (ffa4d47)

🔍 Preview build

11 files changed · ± 11 modified

±Modified

• c-api/type.html
• library/datatypes.html
• library/difflib.html
• library/functions.html
• library/pprint.html
• library/ssl.html
• library/unittest.mock.html
• library/xml.html
• tutorial/stdlib2.html
• whatsnew/3.15.html
• and 1 more...

[hugovk]

Also reverted pdb, it imports it via pyrepl:

[JelleZijlstra]

Yes, pdb also seemed questionable to me since if you use pdb you'll almost certainly want the prompt, which will give you colors.

[JelleZijlstra]

json.tool is also unnecessary, it uses colorize in main() which is the only interface to that module.

I haven't looked much into profiling, are there plausible code paths where that is being used that don't go through colorize? Same for unittest and doctest.

difflib and traceback seem OK, they're broad libraries and there are plenty of functions in there that don't need color.

[bedevere-app]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[JelleZijlstra]

A couple still seem questionable but the cost of an extra lazy import isn't that high, so I'm OK with this going in.

[hugovk]

Thanks all!