Python argparse: How to make an initial parameter determine how many parameters come after?-CodePudding

I'd like to do the following, where the type specified dictates what parameters I can use after.

For example, for cmd1, I'd expect a param1 and param2.

For cmd2, I'd expect a param3, param4, param5, and param6.

For cmd3, I'd expect no parameters.

If I don't specify the expected parameters, an error should be shown.

Also, is there someway I could make it so that issuing a -h would show the different combinations allowed?

In all situations, there may be other tags that could be specified, such as --id 5 or --config 1.

Is this possible with python's argparse?

I.e.,

python test.py --type cmd1 param1 param2 --id 5

python test.py --config 2 --type cmd2 param3 param4 param5 param6

python test.py --type cmd3 --config 1

CodePudding user response：

This use of subcommands will get most of what you want. Read the docs for explainations

#python test.py --type cmd1 param1 param2 --id 5
#python test.py --config 2 --type cmd2 param3 param4 param5 param6
#python test.py --type cmd3 --config 1

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--config', type=int)
parser.add_argument('--id', type=int)
sp = parser.add_subparsers(dest='type', required=True)
sp1 = sp.add_parser('cmd1')
sp1.add_argument('param1')
sp1.add_argument('param2')
sp2 = sp.add_parser('cmd2')
sp2.add_argument('parame1')
# etc
sp3 = sp.add_parser('cmd3')

args = parser.parse_args()
print(args)

test cases

1535:~/mypy$ python3 stack70763135.py -h
usage: stack70763135.py [-h] [--config CONFIG] [--id ID] {cmd1,cmd2,cmd3} ...

positional arguments:
  {cmd1,cmd2,cmd3}

optional arguments:
  -h, --help        show this help message and exit
  --config CONFIG
  --id ID

1535:~/mypy$ python3 stack70763135.py --id 5 cmd1 foo1 foo2
Namespace(config=None, id=5, param1='foo1', param2='foo2', type='cmd1')
1535:~/mypy$ python3 stack70763135.py --config 2 cmd2 foo1
Namespace(config=2, id=None, parame1='foo1', type='cmd2')
1536:~/mypy$ python3 stack70763135.py --config 3 cmd3
Namespace(config=3, id=None, type='cmd3')

The help's might be more fragmented that what you want, but the info is all there.

id and config have to come before the cmd entries.

CodePudding user response：

You should be able to use nargs, I believe. For example:

parser.add_argument('--cmd1', nargs=2)  # expects 2 parameters for this argument

nargs will save the parameters into a list (even if you set it to 1!). There are even special characters you can use for nargs, such as doing nargs='?' to get an indeterminate number of parameters.

CodePudding user response：

this should work:

parser.add_argument("--cmd1",nargs=2)
args = parser.parse_args()
print(args.cmd1)

and running it:

>>> py parser.py --cmd1 onlyoneargument
usage: RecFcs.py [-h] [--cmd1 CMD1 CMD1]
RecFcs.py: error: argument --cmd1: expected 2 arguments

if we provide 2 arguments

>>> py parser.py --cmd1 one two
["one","two"]