`_suggestions` module missing on Windows, untested

[devdanzin]

Bug report

Bug description:

The _suggestions module isn't available in Windows builds because it's missing from PC/config.c. Since it's not tested and only imported in traceback.py in a try: block guarding against ImportError, it's easy to not detect that it's missing.

If there is no objection, I'll create a PR adding the _suggestions module to PC/config.c (and perhaps config_minimal.c) plus basic tests to detect whether it's available and working as intended.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-131712: Build _suggestions extension on Windows #131759
• [3.13] gh-131712: Build _suggestions extension on Windows (GH-131759) #131790

[vstinner]

Oh right, it should be available on Windows as well. Don't we have functional tests for this feature in test_traceback?

[devdanzin]

Don't we have functional tests for this feature in test_traceback?

We do, but traceback.py has a Python implementation that is automatically used if _suggestions fails to import:

cpython/Lib/traceback.py

Lines 1538 to 1550 in f1967e7

	try:
	import _suggestions
	except ImportError:
	pass
	else:
	return _suggestions._generate_suggestions(d, wrong_name)
	# Compute closest match
	if len(d) > _MAX_CANDIDATE_ITEMS:
	return None
	wrong_name_len = len(wrong_name)
	if wrong_name_len > _MAX_STRING_SIZE:

[zooba]

How significant is this module's size/load time/impact?

Since it's only ever going to be used for interactive mode, I think I'd prefer it to be its own extension module, so that we don't pay any cost for it in normal use.

[devdanzin]

Since it's only ever going to be used for interactive mode

I think suggestions are provided for non-interactive use too, aren't they?

I think I'd prefer it to be its own extension module

That'd probably be above my skill level, so if anyone wants to tackle this feel free to.

[vstinner]

Yes, suggestions are also used when running a script.

demo.py:

demo = 1
print(dmo)

Python suggests Did you mean: 'demo'?:

$ ./python demo.py 
Traceback (most recent call last):
  File "/home/vstinner/python/main/demo.py", line 2, in <module>
    print(dmo)
          ^^^
NameError: name 'dmo' is not defined. Did you mean: 'demo'?

[zooba]

It's still not a requirement for production code, so not having it loaded until it's needed would be better.

That said, I just looked at the size of the module and it's tiny. So no concerns about packing it into the main DLL.

[vstinner]

That said, I just looked at the size of the module and it's tiny. So no concerns about packing it into the main DLL.

@devdanzin: Do you feel able to make this change? Or do you want me to have a look?

[devdanzin]

If you tackle this one, I'll use the time to try to fix up my in-flight PRs that I've been too slow to update, thanks!

[vstinner]

I wrote #131759 to build the _suggestions extension on Windows.