Show off your Python chops and compete with others

Steven D'Aprano steve+comp.lang.python at pearwood.info
Fri Nov 8 06:26:18 CET 2013


On Thu, 07 Nov 2013 22:05:14 -0600, Tim Chase wrote:

> On 2013-11-07 21:18, Roy Smith wrote:
>> It's not a shifting goalpost.  My original statement was that:
>> 
>> def foo():
>>    raise Exception
>> 
>> defines a function which 1) has no explicit return statement and 2)
>> does not return None.  I stand by that statement.  There is no possible
>> codepath, no possible calling sequence, no possible execution
>> environment, which will cause that function to return None.
> 
> Well, for varying definitions of "that function", you can do
[snip modified functions]
> Beyond that, I'm sure one could resort to bytecode hacking to have "that
> function" skip the raise...

Now who's shifting the goalposts? Whether you edit the function's source 
code, wrap it in a decorator, or hack it's byte-code, it's not the same 
function as the one Roy showed above by any reasonable definition of "the 
same". As an intellectual exercise of how one might subvert the standard 
semantics of the Python compiler, it is interesting to consider (say) 
byte-code hacks that turn this source code:

def foo():
    raise Exception

into something that returns None, but by the same logic one might say 
that this function:

def spam():
    return 42

connects to some database over the Internet and deletes any table 
containing more than seven records. If we're going to allow those sorts 
of debating shenanigans, the obvious counter is "yes, but when I said 
that the function doesn't return None, I actually meant that it doesn't 
solve the Halting Problem, and it still doesn't do that, so I win nyah 
nyah nyah".



-- 
Steven



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