As you have it, the argument w is expecting a value after -w on the command line. If you are just looking to flip a switch by setting a variable True or False, have a look here (specifically store_true and store_false)

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('-w', action='store_true')

where action='store_true' implies default=False.

Conversely, you could haveaction='store_false', which implies default=True.

Yes.

You have multiple solutions:

• As Mrav mentioned, you can use the system argument (sys.argv[0...])

• Or use argparse. From the documentation (which is python3 compliant), you can do this way:

  if __name__ == '__main__':
      parser = ArgumentParser()
      parser.add_argument('file')
      parser.add_argument('revs', metavar='N', type=int, nargs='+', help='revisions')
      res = parser.parse_args()
      pprint(res)
  

And you can see the result:

$ ./test.py  settings.json 1 2 3
Namespace(file='settings.json', revs=[1, 2, 3])

The premise behind your question is mistaken.

>>> import argparse
>>> p = argparse.ArgumentParser()
>>> p.add_argument('-a')
>>> p.parse_args()
Namespace(a=None)

The -a argument is already optional by default (you don't need required=False), and its default is already None, ensuring that args.a exists without any manual intervention.

You have to opt-in to having no default at all.

>>> p.add_argument("-b", default=argparse.SUPPRESS)
>>> p.parse_args()
Namespace(a=None)

So yes, it probably is a good idea to have some default, and argparse acknowledges that by providing one.

You can do this with nargs='?':

One argument will be consumed from the command line if possible, and produced as a single item. If no command-line argument is present, the value from default will be produced. Note that for optional arguments, there is an additional case - the option string is present but not followed by a command-line argument. In this case the value from const will be produced.

Your three cases would give:

1. The default value;
2. The const value; and
3. '~/some/path'

respectively. For example, given the following simple implementation:

from argparse import ArgumentParser

parser = ArgumentParser()
parser.add_argument('-t', nargs='?', default='not present', const='present without value')

print(parser.parse_args().t)

You'd get this output:

$ python test.py
not present

$ python test.py -t
present without value

$ python test.py -t 'passed a value'
passed a value