Need an example of Python ExceptionGroups

[cclauss]

https://docs.python.org/3/library/exceptions.html#exception-groups (New in Python 3.11)

ExceptionGroups are useful for validating data and telling the user of multiple failures.

For example, if we are examining a string to see if it qualifies as a strong password (#10885) we want to see if it

• is long enough
• not too long
• has lowercase characters
• has uppercase characters
• has acceptable special characters
• does not have unacceptable special characters
• does not have too much repetition

If each of these raised a separate exception then we could use an ExceptionGroup to tell the user all of the problems at once. We could tell them that the proposed password is too short and has no uppercase characters and has a ~ which is an unacceptable special character.

The contribution should solve a normal algorithm problem but should an ExceptionGroup to provide detailed feedback.

[vil02]

Hi @cclauss,

is this something what you are looking for?

from typing import List, Tuple, Callable
from collections import Counter


class PasswordTooShort(Exception):
    pass


class PasswordTooLong(Exception):
    pass


class NoLowercaseCharacter(Exception):
    pass


class NoUppercaseCharacter(Exception):
    pass


class NoSpecialCharacter(Exception):
    pass


class UnacceptableSpecialCharacter(Exception):
    pass


class TooMuchRepetition(Exception):
    pass


def _check_repetition(password: str, max_repetition: int) -> bool:
    count = Counter(password)
    return any(_ > max_repetition for _ in count.values())


def validate_password(password: str) -> None:
    checks: List[Tuple[Callable[[str], bool], Exception]] = [
        (lambda pwd: len(pwd) < 8, PasswordTooShort("Password is too short.")),
        (lambda pwd: len(pwd) > 20, PasswordTooLong("Password is too long.")),
        (
            lambda pwd: not any(c.islower() for c in pwd),
            NoLowercaseCharacter("Password has no lowercase characters."),
        ),
        (
            lambda pwd: not any(c.isupper() for c in pwd),
            NoUppercaseCharacter("Password has no uppercase characters."),
        ),
        (
            lambda pwd: not any(c in "1234567890" for c in pwd),
            NoSpecialCharacter("Password has no acceptable special characters."),
        ),
        (
            lambda pwd: any(c in ",~@" for c in pwd),
            UnacceptableSpecialCharacter(
                "Password has unacceptable special characters."
            ),
        ),
        (
            lambda pwd: _check_repetition(pwd, 2),
            TooMuchRepetition("Password has too much repetition."),
        ),
    ]

    errors = [error for predicate, error in checks if predicate(password)]

    if errors:
        raise ExceptionGroup("Password Validation Errors", errors)


if __name__ == "__main__":
    try:
        validate_password("passssw~rd1")
    except ExceptionGroup as e:
        for exception in e.exceptions:
            print(exception)