Decorators won't catch exceptions

[bytestorm]

Test code:

from functools import wraps


def catch_all(fn):
    @wraps(fn)
    def wrapper(*args, **kwargs):
        try:
            return fn(*args, **kwargs)
        except:
            log.error(f"gotcha")
            #raise
    return wrapper


@service('exception_test.test1')
def test1(**kwargs):
    try:
        raise Exception("will be caught")
    except:
        log.error("this is fine")
        #raise
# result = this is fine


@service('exception_test.test2')
@catch_all
def test2(**kwargs):
    raise Exception("will NOT be caught")
# result = exception

Expected:
"gotcha" error in logs when running exception_test.test2

Actual Result:
Exception in <file.exception_test.test2> line 32: raise Exception("will NOT be caught") ^ Exception: will NOT be caught

[dmamelin]

The issue isn’t with decorators, but with the error-handling subsystem in general. This code will also raise an exception:

def run():
    raise Exception("will NOT be caught")


def catch_all():
    try:
        return run()
    except:
        log.info(f"gotcha")

catch_all()

But changing the code to this (using an intermediate variable) makes it work as expected.

def catch_all():
    try:
        val = run()
        return val
    except:
        log.info(f"gotcha")

Working on an exception handling rework.

[bytestorm]

that is... unexpected =)
thanks for this workaround

but there's always a "but".
I assume it's the same issue, but maybe it'll be useful for some test cases for you since you're reworking exception handling...

functools.wraps adds another layer to the issue and makes the workaround useless

see the code

from functools import wraps

def catch_all(fn):
    @wraps(fn)
    def wrapper(*args, **kwargs):
        try:
            r = fn(*args, **kwargs)
            return r
        except:
            log.error(f"gotcha (nope)")
            #raise
    return wrapper

def catch_all_fixed(fn):
    #@wraps(fn) <- this is the culprit
    def wrapper(*args, **kwargs):
        try:
            r = fn(*args, **kwargs)
            return r
        except:
            log.error(f"gotcha")
            #raise
    return wrapper

@service('exception_test.test1')
@catch_all
def test1(**kwargs):
    raise Exception("will NOT be caught")
# result = exception

@service('exception_test.test2')
@catch_all_fixed
def test2(**kwargs):
    raise Exception("works fine")
# result = gotcha

[dmamelin]

Thanks for the very helpful code example - it will be very useful.