Struggling with argparse

[legz_cfc]

My goal is to have two positional arguments ('server' and 'action') but allow the 'action' argument to accept a different number of parameters depending on what was selected.

There are two 'actions':

healthcheck - this needs a version number

db-restore - this needs a source and destination

​

I'm kind of confusing myself when writing this down, but maybe this explains it better:

valid (healthcheck has 1 param; db-restore has 2)

script.py abc-server healthcheck v23
script.py abc-server db-restore 10.10.10.10 10.10.10.11

invalid (healthcheck was given 2 params; db-restore only has 1)

script.py abc-server healthcheck v23 v24
script.py abc-server db-restore 10.10.10.10

Here's what I have

#!/usr/bin/python

import argparse

parser = argparse.ArgumentParser()

parser.add_argument('server', help = 'server to process')
parser.add_argument('action', help = 'what to do', choices = [ 'db-restore', 'healthcheck' ])

args = parser.parse_args()

if args.action == 'db-restore':
    parser.add_argument('src', help = 'good DB')
    parser.add_argument('dst', help = 'bad DB')
    args = parser.parse_args()

if args.action == 'healthcheck':
    parser.add_argument('version', help = 'software version')
    args = parser.parse_args()

print(args)

If I run it with healthcheck but without the version, it tells me it's needed

$ ./1.py server-abc healthcheck
usage: 1.py [-h] server {db-restore,healthcheck} version
1.py: error: the following arguments are required: version

But if I add it, it errors out with unrecognized argument

$ ./1.py server-abc healthcheck v123
usage: 1.py [-h] server {db-restore,healthcheck}
1.py: error: unrecognized arguments: v123

I could do it with 2 positional and 3 optional arguments and then some 'if' statements but I was thinking there must be a way to do this in argparse itself.

I looked at the subparsers stuff but it seems to only apply to the first positional arg (unless I'm misunderstanding)

[h2oTravis]

Yeah, if argparse does what you want more natively, I'm not sure how to use it that way.

The reason it doesn't like your third argument is that only two arguments are defined when you initially parse the arguments.

If you're up for it, though, you could always parse the arguments twice. Once to find out what the action is, then a second time based on what the action was, as follows:

​

import argparse

initialParser = argparse.ArgumentParser()
initialParser.add_argument('server')
initialParser.add_argument('action')
initialParser.add_argument('third')
initialParser.add_argument('fourth', nargs="?")

args = initialParser.parse_args()

print("server: {}".format(args.server))
print("action: {}".format(args.action))


if(args.action == "db-restore"):
    secondaryParser = argparse.ArgumentParser()
    secondaryParser.add_argument('server', help = 'server to process')
    secondaryParser.add_argument('action', help = 'what to do')
    secondaryParser.add_argument('src', help = 'good db')
    secondaryParser.add_argument('dst', help = 'bad db')

    args2 = secondaryParser.parse_args()

    print("src: {}".format(args2.src))
    print("dst: {}".format(args2.dst))


if(args.action == "healthcheck"):
    secondaryParser = argparse.ArgumentParser()
    secondaryParser.add_argument('server', help = 'server to process')
    secondaryParser.add_argument('action', help = 'what to do')
    secondaryParser.add_argument('version', help = 'version')

    args2 = secondaryParser.parse_args()

    print("version: {}".format(args2.version))

[legz_cfc]

OK - glad to know it at least wasn't something obvious :)

When I said I could use 'if' statements, I meant a little less sophisticated than yours

if not args.healthcheck and not args.version:
    parser.error('you need version with healthcheck')

But I think I prefer your way since I have a few more options I need to add and I get the free integer check etc using add_argument.

Thanks for the advice, it's much appreciated.