Parsing boolean values with argparse

I would like to use argparse to parse boolean command-line arguments written as “–foo True” or “–foo False”. For example:

my_program --my_boolean_flag False

However, the following test code does not do what I would like:

import argparse
parser = argparse.ArgumentParser(description="My parser")
parser.add_argument("--my_bool", type=bool)
cmd_line = ["--my_bool", "False"]
parsed_args = parser.parse(cmd_line)

Sadly, parsed_args.my_bool evaluates to True. This is the case even when I change cmd_line to be ["--my_bool", ""], which is surprising, since bool("") evalutates to False.

How can I get argparse to parse "False", "F", and their lower-case variants to be False?

Answer

This is actually outdated. For Python 3.7+, Argparse now supports boolean args (search BooleanOptionalAction).

The implementation looks like this:

import argparse

ap = argparse.ArgumentParser()

# List of args
ap.add_argument('--foo', default=True, type=bool, help='Some helpful text that is not bar. Default = True')

# Importable object
args = ap.parse_args()

One other thing to mention: this will block all entries other than True and False for the argument via argparse.ArgumentTypeError. You can create a custom error class for this if you want to try to change this for any reason.