Add colour to defaults in `argparse` help

[hugovk]

Feature or enhancement

Proposal:

argparse help is in colour in Python 3.14:

The defaults are also in the same plaintext as the main help, but some other CLIs use another colour.

Typer defaults are light grey:

Composer defaults are yellow:

For argparse, I suggest having "(default: " and ")" in grey, as they're not so important (and always the same). And the default value itself in (non-bold) yellow, to mirror the (bold) yellow of the label, where the default is sort of slotting into. For example, "pretty" is the default format, and the other choices are also in yellow:

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-141679: Add colour to defaults in argparse help #141680

[serhiy-storchaka]

Would not using too much colors distract and make it hard to read?

Some programs that use argparse include "(default: ...)" with literal description in the argument help. Some programs use %(default)s in the argument help. Now they will be different from the generated ones.

[alexprengere]

I think this is a great addition!

As someone who use %(default)s a lot to describe options, I would be glad to have similar colors applied when interpolating such variables. I can open another issue to that effect, and probably work on a PR, if this seems like a good idea.