Error:

argument --fuzzMongodConfigs: invalid choice: 'normal' (choose from n, o, r, m, a, l)

Description:

Python 3.12+ changed how argparse validates the choices parameter, exposing a latent bug in our code.

The Bug in Our Code:
We have choices=("normal") in our argparse argument definition. In Python, ("normal") without a trailing comma is NOT a tuple—it's just the string "normal" with parentheses. To create a single-element tuple, you need ("normal",) with a trailing comma.

Why It Worked in Python 3.11:

# Python 3.11 argparse _check_value() method:
if action.choices is not None and value not in action.choices:
    raise error

# With choices="normal" (a string), this becomes:
if "normal" not in "normal":  # False, because substring match
    raise error  # Doesn't raise - validation passes

The in operator with strings checks for substrings, so "normal" in "normal" is True, making the validation pass accidentally.

Why It Fails in Python 3.12+:

# Python 3.12+ argparse _check_value() method:
if isinstance(choices, str):
    choices = iter(choices)  # Convert string to character iterator
if value not in choices:
    raise error

# With choices="normal" (a string), this becomes:
choices = iter("normal")  # ['n', 'o', 'r', 'm', 'a', 'l']
if "normal" not in ['n', 'o', 'r', 'm', 'a', 'l']:  # True!
    raise error  # Raises error - validation fails

Python 3.12+ now explicitly converts string choices into an iterator over individual characters. The full string "normal" is not in the list of individual characters ['n', 'o', 'r', 'm', 'a', 'l'], so validation fails with the error message showing each character as a separate choice.

References:

• Python 3.11 argparse.py _check_value method
• Python 3.13 argparse.py _check_value method