python - Check if argparse optional argument is set or not

Question

I would like to check whether an optional argparse argument has been set by the user or not.

Can I safely check using isset?

Something like this:

if(isset(args.myArg)):
    #do something
else:
    #do something else

Does this work the same for float / int / string type arguments?

I could set a default parameter and check it (e.g., set myArg = -1, or "" for a string, or "NOT_SET"). However, the value I ultimately want to use is only calculated later in the script. So I would be setting it to -1 as a default, and then updating it to something else later. This seems a little clumsy in comparison with simply checking if the value was set by the user.

Answer 1

I think that optional arguments (specified with --) are initialized to None if they are not supplied. So you can test with is not None. Try the example below:

import argparse

def main():
    parser = argparse.ArgumentParser(description="My Script")
    parser.add_argument("--myArg")
    args, leftovers = parser.parse_known_args()

    if args.myArg is not None:
        print "myArg has been set (value is %s)" % args.myArg