how can argparse set default value of optional parameter to null or empty?

Question

I am using python argparse to read an optional parameter that defines an "exemplar file" that users sometimes provide via the command line. I want the default value of the variable to be empty, that is no file found.

parser.add_argument("--exemplar_file", help = "file to inspire book", default = '')

Will this do it?

Answer 1

Just don't set a default:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--exemplar_file', help='file to inspire book')

args = parser.parse_args()

print(args.exemplar_file)

# Output:
# None

Answer 2

The default default is None (for the default store action). A nice thing about is that your user can't provide that value (there's no string that converts to None ). It is easy to test

 if args.examplar_file is None:
     # do your thing
     # args.exampler_file = 'the real default'
 else:
     # use args.examplar_file

But default='' is fine. Try it.

Answer 3

I think you are looking for this:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("-f", "--fix", action="store_true",
                help="increase output verbosity")
args = parser.parse_args()
if args.fix: #this is True for python file_name.py -f
    print("fix is ON")
else: #it will trigger if python file_name.py
    print("fix is OFF")

'action' enable args.fix to use as None. For more info: https://docs.python.org/3/howto/argparse.html