[FIXED] How to use optional argumnets without - or --(dash)

Issue

i want to use the optional arguments without - or --,

want to achive something like this:

scriptname install <other options>
scriptname uninstall <other options>

my code:

parser = argparse.ArgumentParser()
parser.add_argument("install","INSTALL",action='store_true',help="INSTALL SOMETHING",default="")
parser.add_argument("uninstall","UNINSTALL",action='store_true',help="UNINSTALL SOMETHING",default="") 

args = parser.parse_args()

if args.install:
     install logic

if args.uninstall:
     uninstall logic

getting the error below

ValueError: invalid option string 'install': must start with a character '-'

Solution

A 'store_true' action does not take any arguments (nargs=0). A positional with that action is always true. And it will reject commandline strings like 'install' as unrecognized.

---

The dash is part of the definition of an optional. It identifies strings that serve as flags or names, as opposed to values. Without it you are defining a positional, an argument that is identified by position rather than a flag string.

So the normal optionals definitions would be:

parser.add_argument("--install",action='store_true',help="INSTALL SOMETHING")
parser.add_argument("--uninstall",action='store_true',help="UNINSTALL SOMETHING") 

You could put those in a mutually exclusive group. With store_true the default is False, and if the flag is provided, without any argument, the attribute is set of True.

store_true is allowed with positionals, but doesn't make sense. A positional is required, so you can't get a False value.

You could define a positional with choices:

parser.add_argument('foo', choices=['install', 'uninstall'], help='...')

Then args.foo will have ones of those two string values.

The suggested use of subparsers is a variant on this choices positional - one where the action type is a special one that triggers a new parser.

Answered By - hpaulj