How to Parse Boolean Values Accurately with `argparse`?

Parsing Boolean Values with argparse

When utilizing argparse to parse boolean command-line arguments, it's common to encounter scenarios where the desired behavior differs from the actual output. This occurs when arguments are specified as "--foo True" or "--foo False."

To address this issue, it's essential to delve deeper into the code:

<code class="python">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)</code>

Surprisingly, despite specifying "False" as the argument, parsed_args.my_bool evaluates to True. This anomaly also persists when cmd_line is modified to ["--my_bool", ""], which should logically evaluate to False.

Resolution

To overcome this challenge and accurately parse boolean values, one recommended approach is to adopt the more conventional style:

command --feature

and

command --no-feature

argparse effortlessly supports this format:

Python 3.9 and Above:

<code class="python">parser.add_argument('--feature', action=argparse.BooleanOptionalAction)</code>

Python Below 3.9:

<code class="python">parser.add_argument('--feature', action='store_true')
parser.add_argument('--no-feature', dest='feature', action='store_false')
parser.set_defaults(feature=True)</code>

Alternately, if the "--arg " format is preferred, ast.literal_eval or a custom function, such as the following, can be utilized as the "type" parameter:

<code class="python">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?</code>

The above is the detailed content of How to Parse Boolean Values Accurately with `argparse`?. For more information, please follow other related articles on the PHP Chinese website!