I would like to have a optional argument that will default to a value if only the flag is present with no value specified, but store a user-specified value instead of the default if the user specifies a value. Is there already an action available for this?
An example:
python script.py --example
# args.example would equal a default value of 1
python script.py --example 2
# args.example would equal a default value of 2
I can create an action, but wanted to see if there was an existing way to do this.
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 argumentsconst=1
sets the default when there are 0 argumentstype=int
converts the argument to intIf 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)