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I think this must be easy but I do not get it.

Assume I have the following arparse parser:

import argparse parser = argparse.ArgumentParser( version='pyargparsetest 1.0' ) subparsers = parser.add_subparsers(help='commands') # all all_parser = subparsers.add_parser('all', help='process all apps') # app app_parser = subparsers.add_parser('app', help='process a single app') app_parser.add_argument('appname', action='store', help='name of app to process')

How can I identify, which subparser was used? calling:

print parser.parse_args(["all"])

gives me an empty namespace:

Namespace()
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  • 4
    This question IMHO has better answer then the one considered original. Commented Feb 26, 2014 at 19:34
  • 4
    The supposed duplicate is not helpful to this question Commented May 25, 2019 at 17:16

2 Answers 2

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A simpler solution is to add dest to the add_subparsers call. This is buried a bit further down in the documentation:

[...] If it is necessary to check the name of the subparser that was invoked, the dest keyword argument to the add_subparsers() call will work

In your example replace:

subparsers = parser.add_subparsers(help='commands')

with:

subparsers = parser.add_subparsers(help='commands', dest='command')

Now if you run:

print parser.parse_args(["all"])

you will get

Namespace(command='all')
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6 Comments

This seems like the correct way, as it works like the dest param on any other argument (only it defaults to None, rather than being pulled from the --longopt value). Using set_defaults seems inappropriate for this (but useful for other things)
This is the correct answer! Would be nice to have an example how to test the "command" value.
BTW if there is function in the same class by the name of the command one could do: "getattr(self, args.command)()" to execute it by name!
Can I somehow get the subparser itself instead of just its name ?
The problem with this answer is that the dest variable will contain the alias used (when aliases are in play), not the command name itself. For such cases, set_defaults can help.
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Edit: Please see quornian's answer to this question, which is better than mine and should be the accepted answer.

According to the argparse documentation the result of parser.parse_args(...) will "only contain attributes for the main parser and the sub parser that was selected". Unfortunately this may not be enough information to determine which sub parser was used. The documentation recommends using the set_defaults(...) method on the sub parser to solve this problem.

For example, I've added calls to set_defaults() to your code:

import argparse parser = argparse.ArgumentParser( version='pyargparsetest 1.0' ) subparsers = parser.add_subparsers(help='commands') # all all_parser = subparsers.add_parser('all', help='process all apps') all_parser.set_defaults(which='all') # app app_parser = subparsers.add_parser('app', help='process a single app') app_parser.add_argument('appname', action='store', help='name of app to process') app_parser.set_defaults(which='app')

Now if you run

print parser.parse_args(["all"])

The result is

Namespace(which='all')

Check out the add_subparsers() documentation for more information and another example.

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5 Comments

set_defaults is useful, like in the docs' example where it uses it to bind a sub-command to a function.. but add_parser(dest='which') appears to be the "correct" way to do this, as it doesn't require repeating the subcommand name
@dbr Yep, you're right. Quornian's answer should be the accepted one.
@dbr, should be add_subparsers(dest='which')
This answer is actually very helpful as the solution provided by @quornian has a flaw when using aliases. The alias will be in the dest variable, not the command name. See also stackoverflow.com/questions/59493715/…
What if you want a custom parameter to be sent from the main function to the subparser handler?

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