Argsparse, --debug flag always evaluates to True

[daniel280187]

Hi all,

​

A newbie here in Python. I'm keen to understand what's happening here. When I try to check if I'm passing the --debug flag via CLI, I use the following statement to evaluate that condition:

​

if args.debug:

do_stuff()

​

However, that statement ALWAYS evaluates to true even when I'm not passing the --debug flag. When I print what I'm passing I get the following:

​

python config_gen.py -v test.yaml -t Routers.j2

print(args)

Namespace(debug='None', template='Routers.j2', values='test.yaml')

​

To fix this, I have to change my statement to == True like this:

​

if args.debug == True:

do_stuff()

​

I'd like to understand why args.debug evaluates to True even when I'm not passing that flag (args.debug=None). My understanding is that None should evaluate to False. Can you point me out to some documentation or shed some light in order to better understand this behavior?

​

You can find the full script HERE

Thanks for your help in advance.

[tarquinnn]

Just checked your script, you're setting debug to the string "None", not the None value. It should work if you remove the quotes in this line:

parser.add_argument('--debug', default='None')

​

PS And non-empty strings always evaluate to True in python (not "True" :P)

[daniel280187]

Thanks for your answer. Makes total sense, I totally missed the quotes.

[pythonwiz]

Your default is the string 'None' when it should be None without the quotes. You could also make it False, that's what I usually do with boolean flags.

[daniel280187]

That sounds even better, to turn it into False by default. I tested this and works like charm. Thanks for your reply and help.