Python: Catching a logging.exception() call

Question

I am trying to catch an exception that is not raised, just logged. Is there any way to do this?

def exampleFunction():
    try:
        x = 1 / 0
    except Exception:
        logging.exception('divide by 0 error here.')

try:
    exampleFunction()
except <condition based on if logging.exception was called>
    print('there was a divide by 0 error when I called exampleFunction()')

I sure hope there isn't. If you're interested in knowing whether an exception occurred, why does exampleFunction silently swallow that exception? — Aran-Fey
– Aran-Fey, Commented Sep 26, 2018 at 23:28
There's probably an awful way to do this with mock. Let me thing... — user2201041
– user2201041, Commented Sep 26, 2018 at 23:29
Basically, the exampleFunction just swallows the exception so it doesn't break any code that calls it by throwing a random exception (thinks the issue is minor/skippable). But in my specific case, I need to treat it as an exception — Michael
– Michael, Commented Sep 26, 2018 at 23:31
@Aran-Fey I have seen this in third party libs who assume that this is an internal error which nobody every wants to catch - unfortunately, they guessed wrong and I needed to catch that exception. — Christian Sauer
– Christian Sauer, Commented Sep 27, 2018 at 8:21

Christian Sauer · Accepted Answer · 2018-09-27 08:20:24Z

2

I assume that exampleFunction is in some horrible third party code that you do not own, otherwise there are lots of better alternatives.

What you can do:

import logging # make sure this is the FIRST import of logging
import horrible_third_party_lib

def catch_log(msg):
   # do something when this is called
old_logging = logging.exception
try:
    logging.exception=catch_log
    horrible_third_party_lib.exampleFunction()
finally:
    logging.exception=old_logging

You can then do everything you want in the function. It's horrible and sensitive to import order, but I have used this and it works (scikit learn does something similarly repugnant..)

answered Sep 27, 2018 at 8:20

Christian Sauer

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3 Comments

Michael Over a year ago

Is there a way to use the function catch_log to actually throw an Exception? Basically, I want to be able to do something where I can raise an Exception in def catch_log and do an except Exception clause in-between the try: and finally:

Christian Sauer Over a year ago

Yes of course, just raise the exception you want to throw

Michael Over a year ago

When I tried raising an Exception in catch_log, it didn't actually end up being caught..

stovfl · Accepted Answer · 2018-09-27 07:53:29Z

0

Question: I am trying to catch an exception
The Questions Title should be rewriten to "I am trying to reraise an exception"

Read Python Documentation#raise
Seems somewhat double work, but you can do it like that:

def exampleFunction():
    try:
        x = 1 / 0
    except Exception as e:
        print("logging.exception({})".format(e))
        raise

try:
    exampleFunction()
except ZeroDivisionError as e:
    print('there was a divide by 0 error when I called exampleFunction()')

Output:

logging.exception(division by zero)
there was a divide by 0 error when I called exampleFunction()

Tested with Python:3.5.3

edited Sep 27, 2018 at 7:53

answered Sep 27, 2018 at 7:29

stovfl

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3 Comments

metmirr Over a year ago

Using raise at the end would be enough to reraise the last exception.

stovfl Over a year ago

@metmirr: Please explaine, which end?

metmirr Over a year ago

I mean this: except Exception as e: print('...'); raise

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