[Python-Dev] PEP 389: argparse - new command line parsing module (original) (raw)

Andrew McNabb amcnabb at mcnabbs.org
Wed Sep 30 22:17:35 CEST 2009

On Wed, Sep 30, 2009 at 02:22:53PM -0400, Barry Warsaw wrote:

Right. I've made it kind of work in Mailman 3, but it would be nice for argparse to support this out of the box. Note that I think you want two forms: foo help subcommand foo subcommand --help to basically print the same help text. This is the way bzr does it for example and it works great.

In some commands, options as well as subcommands can change subsequent parsing. The iptables command is a good example of a command-line program that follows this practice. From the man page:

after [a module name is specified], various extra command line options become available, depending on the specific module. You can specify multiple extended match modules in one line, and you can use the -h or --help options after the module has been specified to receive help specific to that module.

In the case of iptables, module names are specified as options, not as subcommands.

From my cursory reading of the documentation, it looks like argparse can only add subparsers for subcommands. Is there any way to add subparsers based on options instead (as iptables does)?

Also, is it possible to add these subparsers dynamically? For example, you would want to be able to load a module immediately after parsing the name instead of having to keep a predetermined list of all module names. I'm pretty sure that bzr dynamically loads modules this way. Can argparse help with this?

Sorry for all of the questions. I ask them because I have some experience with adding the above features to optparse, and it was a lot of work to get it right. It also seems like there are a lot of programs that need to load modules dynamically. I would be really excited if argparse made this easier than optparse did.

-- Andrew McNabb http://www.mcnabbs.org/andrew/ PGP Fingerprint: 8A17 B57C 6879 1863 DE55 8012 AB4D 6098 8826 6868

More information about the Python-Dev mailing list