catching all but specific exception in python

Question

I have a code base with code like the following:

try:
    do_stuff()
except:
    print "yes, it's catching EVERYTHING"

Unfortunately, I don't have a quick enough way of knowing which types of exceptions can come, and am unable to let the system collapse upon encountering one.

This makes debugging hell.

I would like to make it easier upon myself by letting specific exceptions slip by - things like syntax errors, and others.

Is that possible? to catch everything BUT some specific exceptions?

thanks!

Tryph · Accepted Answer · 2019-05-14 12:41:16Z

4

you could do the following:

try:
    do_stuff()
except (SyntaxError, <any other exception>):
    raise  # simply raises the catched exception
except Exception:
    print "yes, it's catching EVERYTHING"

In addition, unless it is really what is wanted, except should never be used without exception specification since it will also catch KeyboardInterrupt and GeneratorExit. Exception should be specified at least; see the builtin exception hierarchy.

Note that, as @tobias_k stated in its below comment, the SyntaxError is detected before actually running the script, so it should not be needed to catch it.

For the challenge I looked for a way to actually catch a SyntaxError and the only case I found is the following (but there are other cases, see @brunodesthuilliers's comment):

try:
    eval(input('please enter some Python code: '))
except SyntaxError:
    print('oh yeah!')

$ python syntax_error.py
please enter some Python code: /
oh yeah!

My conclusion is that if you need to catch SyntaxError, this means your codebase does some stuffs even uglier than what you showed us... I wish you a lot of courage ;)

edited May 14, 2019 at 12:41

answered May 14, 2019 at 11:53

Tryph

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7 Comments

tobias_k Over a year ago

I think the SyntaxError is not even needed, as those should be detected before running the program, but otherwise, e.g. for special treatment of NameError, fine.

Tryph Over a year ago

@tobias_k I finally found a way to catch a SyntaxError, see the edited answer ;)

bruno desthuilliers Over a year ago

@Tryph : other candidates for a SyntaxError (py2, I leave it to you to check the py3 changes): exec, execfile, compile, ast.literal_eval, ast.parse etc...

bruno desthuilliers Over a year ago

@Tryph oh and yes: you should definitly put the "except should never be used without exception specification" in bold (and even in blod caps as far as I'm concerned). I almost downvoted your post before seeing this part. FWIW, you should edit your example to actually NOT use a bare except ;-)

Tryph Over a year ago

@brunodesthuilliers acknowledged

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