How can I test if a function returned an exception object if I don't know in advance what type of exception has been raised?
def func():
try:
bad_thing_happens # NameError("global name 'bad_thing_happens' is not defined",)
return True
except Exception as e:
return e
result = func()
if result == Exception:
print 'a bad thing happened'
In this case the if statement returns False and I would miss the exception?
Functions returning exceptions instead of raising them or letting them bubble is a Bad Thing.
That said, you can test if an object is an instance of a class using isinstance(object, klass).
The proper way would be to catch the exception outside of the function. For example:
def func():
bad_thing_happens
# NameError("global name 'bad_thing_happens' is not defined",)
return True
try:
result = func()
except NameError:
print("a bad thing happened")
This makes it more clear where the exception is coming from (the function) and avoids the mess of trying to return an exception – after all, exceptions are generally meant to be caught and not returned.
If you cannot change the func() for some reason (for example, it is a part of a third-party library code), you can check the type of the returned value via isinstance():
if isinstance(result, Exception):
print 'a bad thing happened'
If you can change func(), then you should not be returning exceptions - they are meant to be raised (and re-raised), caught and handled (and not handled, as well).
Exceptionis a bad idea. If you don't know the type of exception, you very rarely actually know how to handle it properly... Sometimes the best thing you can do is let your program die, look at the stack trace to figure out why it died and fix the bug/logic so that it doesn't die the next time.