Parsing boolean values with argparse

Question

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 1

I think a more canonical way to do this is via:

command --feature 

and

command --no-feature 

argparse supports this version nicely:

Python 3.9+:

parser.add_argument('--feature', action=argparse.BooleanOptionalAction) 

Python < 3.9:

parser.add_argument('--feature', action='store_true') parser.add_argument('--no-feature', action='store_false') parser.set_defaults(feature=True) 

---

Of course, if you really want the --arg <True|False> version, you could pass ast.literal_eval as the "type", or a user defined function ...

def t_or_f(arg):     ua = str(arg).upper()     if 'TRUE'.startswith(ua):        return True     elif 'FALSE'.startswith(ua):        return False     else:        pass  #error condition maybe?