python argparse mutually_exclusive_group and add_argument_group in a parent processor?

问题

I'm not sure if I've found an argparse bug, or if I'm being obtuse. I researched #45602511 which is how I found it "works" in the top-level case.

I'm trying to use an argument_group to separate out some formatting options (which happen to be mutually exclusive). If things are at the top level of the parser structure, I can nest a mutually_exclusive_group under an argument_group and I get the help behavior I'm expecting:

The following code works fine in Python 3.6.2:

import argparse

parser = argparse.ArgumentParser()
commands = parser.add_subparsers()
hit = commands.add_parser('hit')
miss = commands.add_parser('miss')

parser.add_argument('--summary', action='store_true', help='summarize information')
parser.add_argument('--verbose', action='store_true', help='tell us more')

output_format = parser.add_argument_group("Output format")
styles = output_format.add_mutually_exclusive_group()
styles.add_argument('--plain', dest='style')
styles.add_argument('--green', dest='style')
styles.add_argument('--blue', dest='style')

print(parser.parse_args(['-h']))

which generates the following output:

usage: baz.py [-h] [--summary] [--verbose]
              [--plain STYLE | --green STYLE | --blue STYLE]
              {hit,miss} ...

positional arguments:
  {hit,miss}

optional arguments:
  -h, --help     show this help message and exit
  --summary      summarize information
  --verbose      tell us more

Output format:
  --plain STYLE
  --green STYLE
  --blue STYLE

However, I actually need this help code for a subparser, not at the top level, so my code really looks like this, and argparse ignores the argument_group nesting:

global_options = argparse.ArgumentParser(add_help=False)
global_options.add_argument('--summary', action='store_true', help='summarize information')
global_options.add_argument('--verbose', action='store_true', help='tell us more')

output_format = global_options.add_argument_group("Output format", "ways to foo")
styles = output_format.add_mutually_exclusive_group()
styles.add_argument('--plain', dest='style')
styles.add_argument('--green', dest='style')
styles.add_argument('--blue', dest='style')

parser = argparse.ArgumentParser()
commands = parser.add_subparsers()
hit = commands.add_parser('hit', parents=[global_options])
miss = commands.add_parser('miss', parents=[global_options])

print(parser.parse_args(['hit', '-h']))

producing:

usage: bar.py hit [-h] [--summary] [--verbose]
                  [--plain STYLE | --green STYLE | --blue STYLE]

optional arguments:
  -h, --help     show this help message and exit
  --summary      summarize information
  --verbose      tell us more
  --plain STYLE
  --green STYLE
  --blue STYLE

Output format:
  ways to foo

Am I doing something wrong, or is argparse broken?

回答1:

This problem of a nested mutually exclusive group in a parents has been raised in a couple of bug/issues.

http://bugs.python.org/issue25882, (argparse help error: arguments created by add_mutually_exclusive_group() are shown outside their parent group created by add_argument_group())

and

http://bugs.python.org/issue16807, (argparse group nesting lost on inheritance)

Nesting a mutually exclusive group in an argument group works, but isn't documented. But there is an example of this in the unittesting file, http://bugs.python.org/issue17218, (support title and description in argparse add_mutually_exclusive_group)

Copying groups and actions from a parents is handled by parser._add_container_actions method. The parents mechanism works fine for simple parsers, but it is not heavily used nor is it robust.

Sample subparser creation function

def make_subparser(commands, name):
  sub = commands.add_parser(name)
  sub.add_argument('--summary', action='store_true', help='summarize information')
  sub.add_argument('--verbose', action='store_true', help='tell us more')
  output_format = sub.add_argument_group("Output format", "ways to foo")
  styles = output_format.add_mutually_exclusive_group()
  styles.add_argument('--plain', dest='style')
  styles.add_argument('--green', dest='style')
  styles.add_argument('--blue', dest='style')
return sub

parser = argparse.ArgumentParser()
commands = parser.add_subparsers()
hit = make_subparser(commands,'hit')
miss = make_subparser(commands 'miss')

来源：https://stackoverflow.com/questions/46066374/python-argparse-mutually-exclusive-group-and-add-argument-group-in-a-parent-proc

标签

python

argparse