How to pop the interpreter's stack?

[Ethan Furman]

Steven D'Aprano wrote:
> On Sun, 26 Dec 2010 09:15:32 -0800, Ethan Furman wrote:
> 
>> Steven D'Aprano wrote:
>>> Right. But I have thought of a clever trick to get the result KJ was
>>> asking for, with the minimum of boilerplate code. Instead of this:
>>>
>>>
>>> def _pre_spam(args):
>>>     if condition(args):
>>>         raise SomeException("message")
>>>     if another_condition(args):
>>>         raise AnotherException("message")
>>>     if third_condition(args):
>>>         raise ThirdException("message")
>>>
>>> def spam(args):
>>>     _pre_spam(args)
>>>     do_useful_work()
>>>
>>>
>>> you can return the exceptions instead of raising them (exceptions are
>>> just objects, like everything else!), and then add one small piece of
>>> boilerplate to the spam() function:
>>>
>>>
>>> def _pre_spam(args):
>>>     if condition(args):
>>>         return SomeException("message")
>>>     if another_condition(args):
>>>         return AnotherException("message")
>>>     if third_condition(args):
>>>         return ThirdException("message")
>>>
>>> def spam(args):
>>>     exc = _pre_spam(args)
>>>     if exc: raise exc
>>>     do_useful_work()
>> -1
>>
>> You failed to mention that cleverness is not a prime requisite of the
>> python programmer -- in fact, it's usually frowned upon.  The big
>> problem with the above code is you are back to passing errors in-band,
>> pretty much completely defeating the point of have an out-of-band
>> channel.
> 
> How is that any worse than making _pre_spam() a validation function that 
> returns a bool?
> 
> def spam(args):
>     flag = _pre_spam(args)
>     if flag: raise SomeException()
>     do_useful_work()

Also -1.

> Is that also frowned upon for being too clever?

Frowned upon for being out-of-band, and not as much fun as being clever. 
  ;)  I'm pretty sure you've expressed similar sentiments in the past 
(although my memory could be failing me).

More to the point, the OP had code that said:

   args, kwargs = __pre_spam(*args, **kwargs)

and __pre_spam was either passing back verified (and possibly modified)
parameters, or raising an exception.

~Ethan~