Question

I want this functionality:

$ python program.py add Peter 
'Peter' was added to the list of names.

I can achieve this with --add instead of add like this:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("--add", help="Add a new name to the list of names",
                    action="store")
args = parser.parse_args()
if args.add:
   print "'%s' was added to the list of names." % args.add
else:
   print "Just executing the program baby."

Such that:

$ python program.py --add Peter
'Peter' was added to the list of names.

But when I change --add to add it is no longer optional, how can I still let it be optional yet not have those -- signs? (preferably also using the argparse library)

Answer 1

What you want, is actually called “positional arguments”.
You can parse them like this:

import argparse                                                             
parser = argparse.ArgumentParser()                                             
parser.add_argument("cmd", help="Execute a command",                           
                    action="store", nargs='*')                                 
args = parser.parse_args()                                                     
if args.cmd:                                                                   
    cmd, name = args.cmd                                                       
    print "'%s' was '%s'-ed to the list of names." % (name, cmd)               
else:                                                                          
    print "Just executing the program baby."                                   

Which gives you the ability to specify different actions:

$ python g.py add peter
'peter' was 'add'-ed to the list of names.

$ python g.py del peter
'peter' was 'del'-ed to the list of names.

$ python g.py 
Just executing the program baby.