Python, argparse: different parameters with different number of arguments

Question

I would like to write a Python script called sync that has three or four modes of operation, each receiving a different number of arguments. For example,

sync set_version <build> <version_number>
sync get_version <build>
sync has_started <build_1> <build_2> ... <build_n>

I've tried using argparse's subparsers for each mode of operation:

import argparse

parser = argparse.ArgumentParser(description='Build synchronization mechanism')
subparsers = parser.add_subparsers()

parser_get_version = subparsers.add_parser('get_version')
parser_get_version.add_argument('build')

parser_update_version = subparsers.add_parser('update_version')
parser_update_version.add_argument('build')
parser_update_version.add_argument('version')

args = parser.parse_args()
print args

The problem is that the help message is not reflecting the structure of the arguments of each operation modes. Instead, it simply lists the operation modes:

usage: sync.py [-h] {get_version,update_version} ...

Build synchronization mechanism

positional arguments:
  {get_version,update_version}

optional arguments:
  -h, --help            show this help message and exit

How do I force argparse to display a full help message, with all the subparsers parameters?

This might be relevant: http://stackoverflow.com/questions/14918804/how-to-show-help-for-all-subpasers-in-argparse — jsalonen, Jul 24 '13 at 19:39
You might want to check out [`docopt`](http://docopt.org/) for this job - I hear good things about the library. You give a description in a similar style to the help you normally get, and it automatically parses the command line args into a simple data structure, and it appears to output the help as you want it to. — Gareth Latty, Jul 24 '13 at 19:40

Martijn Pieters · Answer 1 · 2013-07-24T20:16:50.770

Each sub-command has it's own help; try sync.py get_version --help, for example.

You'd have to override the help action yourself, and loop over the subcommands and print help for each. This requires some foibling with internal attributes:

class HelpAction(argparse._HelpAction):
     def __call__(self, parser, namespace, values, option_string=None):
         parser.print_help()

         for group in parser._subparsers._group_actions:
             group.choices.values()[0].print_help()

         parser.exit()

parser = argparse.ArgumentParser(description='Build synchronization mechanism',
                                 add_help=False)
parser.add_argument('-h', '--help', action=HelpAction, default=argparse.SUPPRESS,
    help=argparse._('show this help message and exit'))

You probably want to tweak the output some more though.

That's true, but I'd like to list the help for all the modes of operation together. — Adam Matan, Jul 24 '13 at 19:40

Python, argparse: different parameters with different number of arguments

1 Answers1