Python argparse: default value or specified value

by 
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--example', nargs="?", const=1, type=int)
args = parser.parse_args()
print(args)

% test.py 
Namespace(example=None)
% test.py --example
Namespace(example=1)
% test.py --example 2
Namespace(example=2)
  • nargs="?" means 0-or-1 arguments
  • const=1 sets the default when there are 0 arguments
  • type=int converts the argument to int

If you want test.py to set example to 1 even if no --example is specified, then include default=1. That is, with

parser.add_argument('--example', nargs="?", const=1, type=int, default=1)

then

% test.py 
Namespace(example=1)

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