cleaner way to handle python exceptions?

Question

I'm cleaning up some code, and have run into a handful of situations where there are repetitive cleanup actions in a try/except :

try:
    ...
except KeyError , e :
    cleanup_a()
    cleanup_b()
    cleanup_c()
    handle_keyerror()
except ValuesError , e :
    cleanup_a()
    cleanup_b()
    cleanup_c()
    handle_valueerror()

i'd like to make these a bit more standardized for readability and maintenance. the "cleanup" actions seem to be local to the block , so it's not going to be much cleaner to do the following (though it will standardize it a bit):

def _cleanup_unified():
    cleanup_a()
    cleanup_b()
    cleanup_c()
try:
    ...
except KeyError , e :
    _cleanup_unified()
    handle_keyerror()

except ValuesError , e :
    _cleanup_unified()
    handle_valueerror()

can anyone suggest alternate ways of approaching this ?

I notice that there are very good responses that are actually answering two different questions. Perhaps some clarification could be added as to which you are looking for? — SethMMorton
– SethMMorton, Commented Jul 17, 2013 at 22:15

njzk2 · Accepted Answer · 2013-07-17 21:50:14Z

1

You can differenciate the Error by catching all of them in the same except, and testing the type like this:

try:
    ...
except (KeyError, ValuesError) as e :
    cleanup_a()
    cleanup_b()
    cleanup_c()
    if type(e) is KeyError:
        handle_keyerror()
    else:
        handle_valueerror()

answered Jul 17, 2013 at 21:50

njzk2

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1 Comment

Jonathan Vanasco Over a year ago

thats a good idea. IIRC, it would be better to if isinstance(e,types.KeyError):

mipadi · Accepted Answer · 2013-07-17 21:46:43Z

1

If the cleanup can always run, you can use the finally clause, which runs whether an exception is thrown or not:

try:
  do_something()
except:
  handle_exception()
finally:
  do_cleanup()

If the cleanup should only be run in the event of an exception, something like this might work:

should_cleanup = True
try:
  do_something()
  should_cleanup = False
except:
  handle_exception()
finally:
  if should_cleanup():
    do_cleanup()

answered Jul 17, 2013 at 21:46

mipadi

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1 Comment

Jonathan Vanasco Over a year ago

i thought about your second option (with the should_cleanup flag. it looked less readable for the long term.

Michael Butscher · Accepted Answer · 2013-07-17 21:48:57Z

0

If the except block is always the same, you can write:

try:
    ...
except (KeyError, ValueError) , e :
    cleanup_a()
    cleanup_b()
    cleanup_c()
    handle_keyerror()

answered Jul 17, 2013 at 21:48

Michael Butscher

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1 Comment

njzk2 Over a year ago

the difference is the handle_keyerror and handle_valueerror. The except block is not the same.

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