interstar interstar - 7 months ago 95
Python Question

Python argparse command line flags without arguments

How do I add an optional flag to my command line args?

eg. so I can write

python myprog.py


or

python myprog.py -w


I tried

parser.add_argument('-w')


But I just get an error message saying

Usage [-w W]
error: argument -w: expected one argument


which I take it means that it wants an argument value for the -w option. What's the way of just accepting a flag?

I'm finding http://docs.python.org/library/argparse.html rather opaque on this question.

Answer

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 at http://docs.python.org/dev/library/argparse.html#action (specifically store_true and store_false)

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

Edit: As Sven points out, a default value in this case is superfluous.

Comments