Python argparse how to pass False from the command line?

Question

I am trying to sort out how to pass the boolean value False from the command line to the argparser. My origninal code looked like:

import argparse
parser = argparse.ArgumentParser(allow_abbrev=True)
parser.add_argument('-data', default=True, type=bool, help='uses the history file')
args = parser.parse_args(sys.argv[1:])

From the command line, I typed: python myscript.py -data False

Also variations with single & double quotes around False. When I examine the contents of the args namespace, args.data is always True.

So I changed the argument definition from bool to str, with a string "True" default as shown below:

parser.add_argument('-data', default="True", type=str, help='uses the history file')

I then added some massaging of the args to get the boolean value I really wanted:

if re.search("f", args.data, re.I):
   args.data = False
else:
   args.data = True

This workaround does work. Is there a better way to do this?

`bool` converts any non-empty string to True https://stackoverflow.com/questions/715417/converting-from-a-string-to-boolean-in-python — dashiell, Jun 20 '18 at 18:10
You can also use `store_true` see: https://stackoverflow.com/questions/32884131/framework-argparse-check-if-flag-is-set — Patrick Haugh, Jun 20 '18 at 18:11

orn688 · Answer 1 · 2020-01-20T21:43:21.803

14

You can use the store_false or store_true parameter to add_argument (see the argparse documentation). For example, if you want the default to be True then you could add an argument with action='store_false':

parser.add_argument('--no-data', action='store_false', help="don't use the history file")

Then args.no_data will be False if you run python command.py --no-data and True if you run python command.py without the --no-data argument.

edited Jan 20 '20 at 21:43

answered Jun 20 '18 at 18:17

orn688

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Thanks very much! action='store_false' is what I needed. – John Brearley Jun 21 '18 at 16:25
1

Wouldn't using some other variable name make more sense? Something like `dest='data'` That way, it's not `args.no_data` which is false, but `args.data` – Wassadamo Mar 02 '21 at 10:34

score 5 · Answer 2 · answered Jun 20 '18 at 18:13

5

def my_bool(s):
    return s != 'False'

parser.add_argument('-data',default=True,type=my_bool)

answered Jun 20 '18 at 18:13

dashiell

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Thank you, this is exactly what I needed. I cannot use flags in my application, for now. – jonathanking Feb 18 '20 at 23:12

score 5 · Answer 3 · answered Jun 20 '18 at 18:15

5

If an argument is meant to be a boolean, you should simply use store_true or store_false, so that the presence of the option itself would result in a True or False value, and the absence of the option would result in a False or True value, respectively.

From argparse's documentation:

>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='store_true')
>>> parser.add_argument('--bar', action='store_false')
>>> parser.add_argument('--baz', action='store_false')
>>> parser.parse_args('--foo --bar'.split())
Namespace(foo=True, bar=False, baz=True)

answered Jun 20 '18 at 18:15

blhsing

91,368
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Thanks very much! action='store_false' is what I needed. – John Brearley Jun 21 '18 at 16:24
Can I use both `store_true` and `store_false`? – alper Jul 17 '21 at 19:20
What do you mean to achieve with both options enabled? The value of an option can't be both `True` and `False`. – blhsing Jul 19 '21 at 00:57

Python argparse how to pass False from the command line?

3 Answers3