generic exception handling return value

Question

I am trying to create generic exception handler - for where I can set an arg to return in case of exception.

instead of doing:

try:
    ...
except Exception:
    return list()

try:
    ...
except Exception:
    return dict()

try:
    ...
except Exception:
    return str()

I would like to create system whereby I have a generic exception handler that returns an arg I provide. e.g,

def handler(code, default):
    try:
        code
    except Exception:
        return default

def mains():
    code = <code to execute>
    default = str()
    return handler(code, dafault)

but in a more pythonic way

so you want to have something like "GENERIC_ERROR: problem solved". trial and error type-of problem solving? :-) — baldrunner2049
– baldrunner2049, Commented Nov 3, 2012 at 23:05
I'm confused as to what exactly you want to create. Could you show how this handler of yours would be used in client code? — millimoose
– millimoose, Commented Nov 3, 2012 at 23:07
this code will be in functions that should return a list, or another that returns a dict, or another that returns a number. I want to return a default value of an empty list, empty dict, or 0 in case of exceptions in these functions. — Rich Tier
– Rich Tier, Commented Nov 3, 2012 at 23:08
The "pythonic" way would be not doing this and just using a try..except directly to make the error handling obvious. — millimoose
– millimoose, Commented Nov 3, 2012 at 23:14
@millimoose Not necessarily. DRY is a fairly Pythonic concept. — pydsigner
– pydsigner, Commented Nov 3, 2012 at 23:20

pydsigner · Accepted Answer · 2012-11-04 01:13:25Z

4

A simple decorator will do this for you.

import functools


def catch_wrap(on_err):
    def wrapper(func):
        @functools.wraps(func)
        def inner(*args, **kw):
            try:
                return func(*args, **kw)
            except Exception:
                return on_err
        return inner
    return wrapper

A short example:

@catch_wrap('SPAM!')
def doer():
    """
    YUP
    """
    1 / 0
    return 'EGGS!'


print doer()
print doer.__doc__

edited Nov 4, 2012 at 1:13

answered Nov 3, 2012 at 23:09

pydsigner

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12 Comments

millimoose Over a year ago

It's probably a good idea to use @functools.wraps for code like this.

pydsigner Over a year ago

@millimoose I don't think that wraps would do much extra in this case.

millimoose Over a year ago

@pydisigner Oh, I missed that you're already taking steps to preserve __doc__. I guess because I'm so used to doing that with @wraps. (It does however do more than just __doc__)

pydsigner Over a year ago

@millimoose I just added that :). I don't think that the complexity of @functools.wrap is warranted.

pydsigner Over a year ago

There is a major hole in this; passing bad args will be masked. Time to dig out inspec.getargspec...

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