argparse with multiple flags and arguments - python-3.x

Question

I want my code to be able to call different functions according to the flag and then use the argument passed after the flag as the input to the function.
Example of the expected output:
$ python3 test.py -a 2
4
$ python3 test.py -a human123
<Error message>
$ python3 test.py -h human123
Hello, human123
Here's my sample code:
class Test:
def __init__(self):
pass
def add(self, a):
return a+a
def hello(self, name):
return f"Hello, {name}"
parser = argparse.ArgumentParser()
parser.add_argument('-a', '--add', dest='command', action='store_consts', const='add', nargs=1, help='add a to itself')
parser.add_argument('-h', '--hello', dest='command', action='store_consts', const='hello', nargs=1, help='hello!')
args = parser.parse_args()
t = Test()
if args.command=='add':
print(t.add(args.add))
elif args.command=='sub':
print(t.hello(args.hello))
This sample code currently is doing what I want to achieve. I tried many things to fix the issue from removing the 'consts', changing the action to 'store', changing the value of nargs to '?', etc., however, it keeps giving me different kinds of errors like TypeError, etc.

Answer 1

Simplifying your arguments:
import argparse
class Test:
def __init__(self):
pass
def add(self, a):
return a+a
def hello(self, name):
return f"Hello, {name}"
parser = argparse.ArgumentParser()
parser.add_argument('-a', '--add', help='add a to itself')
parser.add_argument('-b', '--hello', help='hello!') # -h is already taken
args = parser.parse_args()
print(args)
t = Test()
if args.add: # or 'args.add is not None:'
print(t.add(args.add))
elif args.hello:
print(t.hello(args.hello))
test runs:
1936:~/mypy$ python3 stack62702524.py -a testing
Namespace(add='testing', hello=None)
testingtesting
1937:~/mypy$ python3 stack62702524.py -b other
Namespace(add=None, hello='other')
Hello, other
1937:~/mypy$ python3 stack62702524.py
Namespace(add=None, hello=None)
===
Your errors, which you did not show :{ When you get errors, don't just throw up your hands and randomly try alternatives. Read the docs and try to understand the error.
parser.add_argument('-c', action='store_consts', const='hello')
ValueError: unknown action "store_consts"
parser.add_argument('-c', action='store_const', const='hello', nargs=1)
TypeError: __init__() got an unexpected keyword argument 'nargs'
'store_consts' is an name error; with 'store_const' nargs is fixed at 0; you can't change that.
If I add 3 arguments - two store_const and one positional:
parser.add_argument('-c', dest='command', action='store_const', const='add')
parser.add_argument('-d', dest='command', action='store_const', const='hello')
parser.add_argument('foo')
Note the two new command and foo attributes, which you could use in your function call:
1945:~/mypy$ python3 stack62702524.py -c bar
Namespace(add=None, command='add', foo='bar', hello=None)
1945:~/mypy$ python3 stack62702524.py -d bar
Namespace(add=None, command='hello', foo='bar', hello=None)

Answer 2

Typically I use the dest parameter of add_argument to specify the variable name.
For example:
parser.add_argument("-a", "--add", dest="add", required=False, type=str help="some help")
Could be accessed by:
args = parser.parse_args()
print(args.add == "something")
I believe that you need one unique dest per argument.
Also, -h is reserved for help. You may wish to change this to -e or something.
parser.add_argument('-h', '--hello', ...)