Python argparse with subparsers and optional positional arguments

问题

I would like to have a program with subparsers that handles specific arguments while also keep some positional and optional arguments to the previous parsers (In fact what I really want is only one option, I mean, a valid subparser OR a valid local argument).

Example of something I wish to have: Program [{sectionName [{a,b}]}] [{c,d}]. Being c/d incompatible if sectionName was provided and viceversa.

However, the best I could achieve is this test.py [-h] {sectionName} ... [{c,d}]. This means, argparse don't allow me to use the positional arguments c or d without specifying a valid sectionName.

Here is the code:

import argparse

mainparser = argparse.ArgumentParser()
# Subparser
subparser = mainparser.add_subparsers(title="section", required=False)
subparser_parser = subparser.add_parser("sectionName")
subparser_parser.add_argument("attribute", choices=['a', 'b'], nargs='?')
# Main parser positional and optional attributes
mainparser.add_argument("attribute", choices=['c', 'd'], nargs='?')

mainparser.parse_args()

I'm getting crazy with this. Any help would be much appreciated!

Edit: I'm using Python 3.8

回答1:

The subparser object is actually a positional Action, one that takes choices - in this case {'sectionName'}. positinal arguments are filled in the order that they are defined, using the nargs pattern to allocate strings.

Once the main parser gets the 'sectionName' it passes the parsing to subparser_parser. Than handles the rest of the input, such as the {'a','b'} positional. Anything it can't handle is put on the 'unrecognized' list, and control returns main for final processing. main does not do any further argument processing. Thus your attribute argument is ignored.

You could put define a attribute positional before the add_subparsers, but I wouldn't try to make it nargs='?'.

So it's best to define all main arguments before the subparsers, and to use optionals. This will give the cleanest and most reliable parsing.

来源：https://stackoverflow.com/questions/64042616/python-argparse-with-subparsers-and-optional-positional-arguments

标签

python

python-3.x

argparse