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Catch exception from forked subprocess

asked 2021-07-06 15:10:22 +0200

philipp7 gravatar image

I use fork to give certain methods only a fixed time for execution. These methods might, however, raise an exception and I don't know how to catch these. The code:

@fork
def test() :
    raise ValueError("Found a value error")

try :
    test()
except ValueError :
    print("Value error caught")

does not catch the error. Is there a way to do this?

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answered 2021-07-07 09:50:40 +0200

philipp7 gravatar image

My, not so nice, solution is the following: The idea is that we catch the exception e in the forked process and just return it as the object e. Then, after calling this forked process, we check whether the returned value is in fact an exception. If so, we raise it. Of course this has several drawbacks (what if a function really wants to return an exception? also the traceback gets more complicated) but seems to work okay for me. If anyone has a nicer solution, I would be very interested to learn about it!

def encode_exceptions(func, *args, **kwargs) :
    try :
        ret = func(*args, **kwargs)
        return ret
    except Exception as e:
        return e

def decode_exceptions(ret) :
    if isinstance(ret, Exception) :
        raise ret
    else :
        return ret

def fork_func(func, *args, **kwargs) :
    @fork
    def forked_func():
        return encode_exceptions(func, *args, **kwargs)
    ret = forked_func()
    return decode_exceptions(ret) 

def test() :
    raise ValueError("Found a value error")

print(fork_func(test))
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Asked: 2021-07-06 15:10:22 +0200

Seen: 93 times

Last updated: Jul 07 '21