Entering positional argument with argument key?

I want to enter a positional argument with it's key name. Here is my example.py file:

parser = argparse.ArgumentParser()
parser.add_argument('receiver', help="Enter receiver email ID")                    
args = parser.parse_args()

Now I want to enter the the argument as: python3 example.py receiver <argument> I want to use 'receiver' key to enter corresponding argument.