GH-99749: Add optional feature to suggest correct names (ArgumentParser)

[savannahostrowski]

This PR carries #99773 forward with the original author's go-ahead (thanks @abdulrafey38!). This adds the ability for ArgumentParser to offer suggestions for mistyped argument choices or subparser names. This PR adds this as an optional feature via the suggest_on_error param (default: False).

I have opted to not make this configurable at the subparser or argument level and instead at the parser level to keep this simple. We could consider additional granularity but I'm not convinced that this is required at this time.

• Issue: Add “maybe you meant” in argparse choices argument #99749

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📚 Documentation preview 📚: https://cpython-previews--124456.org.readthedocs.build/

[savannahostrowski]

@rhettinger Looks like CI is all green now!

[danielhollas]

This PR adds this as an optional feature via the suggest_on_error param (default: False).

Just wondering, if you choose to make this False by default, then effectively application devs will not be able to use this new feature until they drop support for Python <3.14 (unless I am mistaken?). Maybe it would be "nicer" to make this opt-out instead of opt-in?

If I understood correctly, the main argument against this in the original PR was a concern about adding more import time to argparse module from difflib, but since it is now imported lazily perhaps that is no longer such an issue?

[savannahostrowski]

Right, this would be a new, opt-in feature in 3.14 onward. If we instead made it opt-out, it could unexpectedly change outputs that users depend on (e.g., for tests or other workflows). In general, I think we should be somewhat conservative with changes to argparse to prevent breaking changes.

[serhiy-storchaka]

LGTM.

This PR slightly conflicts with #117766. After merging one of them, the other one should be updated. I am not sure what of them should be merged first.

[rindeal]

This PR slightly conflicts with #117766. After merging one of them, the other one should be updated. I am not sure what of them should be merged first.

A fix should definitely precede a new feature.