gh-141679: Add colour to defaults in argparse help

[hugovk]

• Issue: Add colour to defaults in argparse help #141679

[savannahostrowski]

One comment about the two-color choice - I wonder if it might be a bit busy with the frequent color switching.

But overall, this looks really good and aligns with modern CLIs, IMO. I pretty extensively tested this and I couldn't find any issues. I also think it's fine to not apply color in help text when users might have literally written (default: ).

[mpkocher]

One comment about the two-color choice - I wonder if it might be a bit busy with the frequent color switching.

It would be useful to push these changes and then try to get as much feedback as possible before the 3.15 release. I agree that it does look a little too busy.

I believe it would be good idea to make the ThemeSection (and colorize) public and more clearly define the backwards compatibility rules. This would allow people to set the theme (for argparse) when initializing the ArgumentParser instance.

Not sure if there was a follow up issue created from the "Open Issues" section of #133346 (specifically, clarifying how schema changes of a ThemeSection should be handled).

It should be possible for the user to keep using a theme from 3.14 in future versions of Python without changes. The new color definitions would be automatically taken from the default theme.

In [7]: from _colorize import get_theme

In [8]: t = get_theme().argparse

In [9]: t.action
Out[9]: '\x1b[1;32m'

In [10]: t.default
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[10], line 1
----> 1 t.default

AttributeError: 'Argparse' object has no attribute 'default'

In [11]: t.default_value
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[11], line 1
----> 1 t.default_value

AttributeError: 'Argparse' object has no attribute 'default_value'

[hugovk]

I believe it would be good idea to make the ThemeSection (and colorize) public and more clearly define the backwards compatibility rules. This would allow people to set the theme (for argparse) when initializing the ArgumentParser instance.

Not sure if there was a follow up issue created from the "Open Issues" section of #133346 (specifically, clarifying how schema changes of a ThemeSection should be handled).

When time allows, I think @ambv is planning on a PEP for adding a colorize module for 3.15, and this would be great input for that discussion.