Implement and/or document flags (boolean option) with automatic sub-flags

[flying-sheep]

flags are CLI parameters that take no argument. they usually have an inversion (--no-<name> or +g)

i guess #2 is about customization and short flags/options in general. this is about the automatic version of flag features.

flags with an automatic --no-<name> version would be cool.

import defopt

def my_cmd(legend=True):
    print(legend)

if __name__ == '__main__':
    defopt.run(my_cmd)

$ python my_cmd.py --legend
True
$ python my_cmd.py --no-legend
False

once short options/flags (#2) are there, an automatic flag inversion using +g would also be cool:

$ python my_cmd.py +g
False

[evanunderscore]

I think I initially had reasons for not doing this but they all seem a bit weak now. I like the idea of doing this automatically.

I personally find negations using + to be counter-intuitive, but I'm aware that they're used in a number of places, so I'm not against giving people the option to use them if we can find a simple way of doing it. I'll keep this in mind when looking at #2.

[flying-sheep]

an alternative would be negations using the uppercase short opt.

[evanunderscore]

What's the point of the inverted flags? I know they're used in some places, but they just seem confusing to me. Here's an actual example from pip install -h:

  --compile                   Compile py files to pyc
  --no-compile                Do not compile py files to pyc

Obviously one of these must be the default, but I have no way of telling. Since one of them is implied by not specifying it, why do we need the flag at all?

Here's another flag for the same command:

--no-clean                  Don't clean up build directories.

Since there is no corresponding --clean flag, I know that the default behavior must be to clean up build directories.

[flying-sheep]

with both, the default can be changed anytime (--flag means True, --no-flag means False)

and as the later option trumps, you can override stuff in aliases, …

alias ls='ls -l'

$ ls
drwxr-xr-x 1 phil users  314  6. Mär 12:12 bin/
$ ls -x
bin/

[evanunderscore]

I've had a shot at an implementation of this to use as a discussion point. Take a look at 09bdead.

Some points to discuss:

• This only applies to optional arguments; a positional boolean argument is still specified as something accepted by _parse_bool.
• The help message only shows documentation for the --name flag; the --no-name flag is blank but comes immediately after the other flag so should be clear enough.
• This allows for you to have None or some other value as the default, so neither --name nor --no-name are necessarily implied to match the default behavior (if you really want to do that).

[evanunderscore]

This has been implemented and will be in 2.0. Discussion on how to handle short flags can continue in #2 if necessary.