raise None

Wed Dec 30 19:38:12 EST 2015

On Thu, Dec 31, 2015 at 11:09 AM, Steven D'Aprano <steve at pearwood.info> wrote:
> I have a lot of functions that perform the same argument checking each time:
>> def spam(a, b):
> if condition(a) or condition(b): raise TypeError
> if other_condition(a) or something_else(b): raise ValueError
> if whatever(a): raise SomethingError
> ...
>> def eggs(a, b):
> if condition(a) or condition(b): raise TypeError
> if other_condition(a) or something_else(b): raise ValueError
> if whatever(a): raise SomethingError
> ...
>>> Since the code is repeated, I naturally pull it out into a function:
>> def _validate(a, b):
> if condition(a) or condition(b): raise TypeError
> if other_condition(a) or something_else(b): raise ValueError
> if whatever(a): raise SomethingError
>> def spam(a, b):
> _validate(a, b)
> ...
>> def eggs(a, b):
> _validate(a, b)
> ...
>>> But when the argument checking fails, the traceback shows the error
> occurring in _validate, not eggs or spam. (Naturally, since that is where
> the exception is raised.) That makes the traceback more confusing than it
> need be.

If the validation really is the same in all of them, then is it a
problem to see the validation function in the traceback? Its purpose
isn't simply "raise an exception", but "validate a specific set of
inputs". That sounds like a perfectly reasonable traceback line to me
(imagine if your validation function has a bug).
ChrisA