Unable to assign default values to arguments in Python argparse

Question

I am using Python argparse to take in parameters through the CLI. I have tried using the following but when I don't give any one of the arguments, it gives the output as None. I want then default ones to be the ones provided in const=. Please take a look.

parser = argparse.ArgumentParser()
parser.add_argument('--input', nargs='?', const='testInput')
parser.add_argument('--target', nargs='?', const='testTarget')
parser.add_argument('--msg', nargs='?', const='helloFromTheOtherSide')
args = parser.parse_args()
print args.input

If I don't give input, it prints it as None as I said. I want it to print TestInput instead..

Roland Smith · Accepted Answer · 2017-03-05 12:08:58Z

1

Use the default argument:

parser = argparse.ArgumentParser()
parser.add_argument('--input', nargs='?', default='testInput')
parser.add_argument('--target', nargs='?', default='testTarget')
parser.add_argument('--msg', nargs='?', default='helloFromTheOtherSide')
args = parser.parse_args()
print args.input

answered Mar 5, 2017 at 12:08

Roland Smith

43.8k3 gold badges69 silver badges98 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

hpaulj · Accepted Answer · 2017-03-05 17:13:22Z

0

With

parser.add_argument('--input', nargs='?', default='testInput', const='aConst')

you have a 3 way choice

prog                  # input='testInput'
prog --input          # input='aConst'
prog --input myfile   # input='myfile'

If you don't need that aConst option, omit the nargs='?'. Since it is a flagged argument it is already optional. It doesn't need the `?'.

parser.add_argument('--input', default='testInput')

answered Mar 5, 2017 at 17:13

hpaulj

233k14 gold badges260 silver badges392 bronze badges

Collectives™ on Stack Overflow

Unable to assign default values to arguments in Python argparse

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related