How to use top-level arguments with subparsers in argparse

Question

In Python's argparse, how do you implement top-level arguments while still using commands implemented as subparsers?

I'm trying to implement a --version argument to show the program's version number, but argparse is giving me error: too few arguments because I'm not specifying a sub-command for one of the subparsers.

My code:

import argparse parser = argparse.ArgumentParser() parser.add_argument( '-v', '--version', help='Show version.', action='store_true', default=False ) subparsers = parser.add_subparsers( dest="command", ) list_parser = subparsers.add_parser('list') parser.parse_args(['--version'])

the output:

usage: myscript.py [-h] [-v] {list} ... myscript.py: error: too few arguments

chepner · Accepted Answer · 2015-04-29 14:26:15Z

If you only need version to work, you can do this:

import argparse parser = argparse.ArgumentParser() parser.add_argument( '-v', '--version', action='version', version='%(prog)s 1.0', )

Subparsers won't bother any more; the special version action is processed and exits the script before the parser looks for subcommands.

hpaulj · Accepted Answer · 2015-04-29 22:11:52Z

The subparsers is a kind of positional argument. So normally that's required (just as though you'd specified add_argument('foo')).

skyline's suggestion works because action='version' is an action class that exits after displaying its information, just like the default -h.

There is bug/feature in the latest argparse that makes subparsers optional. Depending on how that is resolved, it may be possible in the future to give the add_subparsers command a required=False parameter. But the intended design is that subparsers will be required, unless a flagged argument (like '-h') short circuits the parsing.

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