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Special casing the formatting of 'store_const' makes me nervous because formatting is already complicated and it doesn't know anything about action types.
But feel free to propose a patch!
In the meantime:
- propagate the default to all the options
You can, of course, do this manually, by specifying default in each of them. And if you use formatter_class=ArgumentDefaultsHelpFormatter, you'll get the defaults in the usage message.
- group the keywords that have the same destination together (?)
- place the default option first (?)
You can achieve both of these by just adding the options in the order that you want them displayed.