How to parse multiple nested sub-commands using python argparse?

Question

I am implementing a command line program which has interface like this:

cmd [GLOBAL_OPTIONS] {command [COMMAND_OPTS]} [{command [COMMAND_OPTS]} ...]
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Answer 1

Another package which supports parallel parsers is "declarative_parser".

import argparse
from declarative_parser import Parser, Argument

supported_formats = ['png', 'jpeg', 'gif']

class InputParser(Parser):
    path = Argument(type=argparse.FileType('rb'), optional=False)
    format = Argument(default='png', choices=supported_formats)

class OutputParser(Parser):
    format = Argument(default='jpeg', choices=supported_formats)

class ImageConverter(Parser):
    description = 'This app converts images'

    verbose = Argument(action='store_true')
    input = InputParser()
    output = OutputParser()

parser = ImageConverter()

commands = '--verbose input image.jpeg --format jpeg output --format gif'.split()

namespace = parser.parse_args(commands)

and namespace becomes:

Namespace(
    input=Namespace(format='jpeg', path=<_io.BufferedReader name='image.jpeg'>),
    output=Namespace(format='gif'),
    verbose=True
)

Disclaimer: I am the author. Requires Python 3.6. To install use:

pip3 install declarative_parser

Here is the documentation and here is the repo on GitHub.