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.
To add an optional argument, simply omit the required parameter in add_argument() .
The store_true option automatically creates a default value of False. Likewise, store_false will default to True when the command-line argument is not present.
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
.
Adding a quick snippet to have it ready to execute:
Source: myparser.py
import argparse parser = argparse.ArgumentParser(description="Flip a switch by setting a flag") parser.add_argument('-w', action='store_true') args = parser.parse_args() print args.w
Usage:
python myparser.py -w >> True
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