Python argparse subparser valid usage?

Question

I am planing to write a command using the argparse library, this is my command structure:

$ python cvs.py -d my_adress local diff -r xyz -N -d details

Here, the local has multiple command grouped to it such as local commit, local add etc. E.g. [-d my_address] is parsed in main and all switches after local diff are parsed together by a function executed for local diff.

Similarly, there is another command group parallel to local; say global.

The switch -d is not mixed with -r. So, the parser parsing -r doesn't know about -d and vice versa.

Is it possible to implement this using argparse? If yes, can somebody suggest me a rough algorithm to do this. If no, What are other possible way to do this in python? Thanks.

Your description is not clear. What do you mean by 'local has multiple command[s] inside it'? Flagged arguments like -d are parsed independently, and can occur in any order. Remember, argparse parses your input, but does not execute it. — hpaulj
– hpaulj, Commented May 19, 2015 at 15:31

Toolforger · Accepted Answer · 2015-05-19 07:03:12Z

See the nargs parameter, namely the '*' option. It won't do a subparse (I do not think that argparse can to that at all), but it will at least group your options so you'll get -d and -r returned as separate options. -N won't be a known option. I don't know whether argparse would consider it an error (which you don't want), or just another parameter of -r.

Your approach might fail. CVS subcommands can have all sorts of one-letter options like -d, -r, etc. (it's a long list). You'll find yourself constantly making hard choices of whether you want to support a specific CVS option as a subcommand or rather use the letter for your cvs.py option.

You could introduce some markup to separate CVS subcommands, i.e. python cvs.py -d my_adress local diff § -r xyz -N. However, that's not a real improvement over cvs -d my_adress local diff; cvs -r xyz -N anymore.

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