B042 has naive definition of exception

[GPHemsley-RELX]

B042 (introduced in #421 / #512) has a naive way of determining whether a class is an exception:

flake8-bugbear/bugbear.py

Lines 1798 to 1802 in 915edea

	def is_exception(s: str):
	for ending in "Exception", "Error", "Warning", "ExceptionGroup":
	if s.endswith(ending):
	return True
	return False

It is based solely on the name of the class, which means it returns True even if the class is not an exception.

For example, if I have a context manager class called FailOnException, it will trigger, even though that class is not an exception at all:

from typing import (ContextManager, TypeVar)
T = TypeVar("T")
class FailOnException(ContextManager[T]): pass

print(FailOnException.__mro__)

(<class '__main__.FailOnException'>, <class 'contextlib.AbstractContextManager'>, <class 'abc.ABC'>, <class 'typing.Generic'>, <class 'object'>)

[cooperlees]

I get the "buggy" nature, but calling something an exception that isn't an exception is misleading right? Probably don't want to do that in Python ...

But open to maybe using inheritance from BaseException etc. to be smarter here if others agree.

[GPHemsley-RELX]

FailOnException is a context manager that catches exceptions and then fails gracefully; it's not calling itself an exception.

I think checking for inheritance from BaseException is the only right way to do this, and indeed is a more Pythonic way.

In Python, all exceptions must be instances of a class that derives from BaseException.