Argparse: is it possible to combine help texts from multiple parsers?

Question

I'm writing a module with custom logging utilities to be imported in other scripts. It's based on the standard-library logging module.

One of these utilities looks like this:

import argparse as ap

def parse_log_args() -> dict:

    log_arg_parser = ap.ArgumentParser(description='Parses arguments that affect logging')
    log_arg_parser.add_argument(
        '--level',
        dest='level',
        help='Sets logging level',
        choices=['DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL']
    )
    log_args, _ = log_arg_parser.parse_known_args()
    return vars(log_args)

This function looks for arguments that have to do with logging (even though only --level is defined for the time being) and parses those independently of (and before) all others so that the logging can be configured early on and used in the rest of the script.

The goal here is to remain flexible and be able to quickly plug-in support for these arguments, both in scripts that expect no other arguments and in those that do.

From the point of view of simply parsing arguments this works: this function runs first, parses --level and then the script-specific parser comes and handles the rest.

The problem, however, is the help text. When I run a script that calls this function with --help it only displays the help text from this first parser and not from the script-specific one. So something like this:

Parses arguments that affect logging

optional arguments:
  -h, --help            show this help message and exit
  --level {DEBUG,INFO,WARNING,ERROR,CRITICAL}
                        Sets logging level

• Is there a way to combine the help-texts from all the ArgumentParser instances in a script?
• Alternatively: Is there a different way to achieve this in a flexible/plug-in kind of way, that is, without modifying existing ArgumentParsers or having to add them to scripts that don't yet use them?

PS: A similar question has been asked before here: Argparse combine --help directives but the proposed ideas don't really solve the problem:

• Define the first parser with add_help=False: This would hide the option from the user which I would prefer not to do.
• Use subcommands somehow: doesn't seem to be applicable here.

Answer 1

I think this might fit the bill:

import argparse

part1 = argparse.ArgumentParser(add_help=False)

#... some parsing takes place ...

part2 = argparse.ArgumentParser(add_help=True, parents=[part1])

part1 parser must be fully initialized for parents to work.

More on the topic: https://docs.python.org/3/library/argparse.html#parents