[Python] Check if ArgParse optional argument is set, default value supplied

I'm trying to check if an optional argument is supplied by the user but I want to set its default value if it is not supplied. If I try to use if statement by exploiting None, the default in help string says None which is incorrect

import argparse
parser = argparse.ArgumentParser(usage=__file__ + " [--options]",
description=__doc__,
formatter_class=argparse.ArgumentDefaultsHelpFormatter)

parser.add_argument("--scheme", choices=["A", "B"])
parser.add_argument("--min-A", type=float, help="Default=5")
parser.add_argument("--min-B", type=float, help="Default=10")
args = parser.parse_args()

if args.scheme == "A":
if args.min_A:
min_A = args.min_A
else:
min_A = 5
else:
if args.min_A:
parser.error("--min-A can only be provided when --scheme is A")

#similar code for B


Here, the help string automatically puts default as None. If I put default as 5, then I'm not able to check whether --min-A has been provided by user because it stores the default instead of None when the option is absent in input.

Any ideas on how to execute this?

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