Are decorators really that different from metaclasses...

[Jeff Shannon]

Paul Morrow wrote:

> Hallvard B Furuseth wrote:
>
>> Yes, I can compare that.  It's fine in a class body, which is executed
>> when the class definition is executed.  When I see it in a function
>> definition, I see a strange use of the assignment operator, which is
>> normally a 'run-time' operator, in a place where it not being executed
>> at run-time.
>>
>
> It's also a 'definition-time' operator, as it often appears in class and
> module definitions.  So why not be consistent and let it appear in
> function definitions too?  What is so outrageous about this idea? On the
> 'strange-meter', does it rank as high as docstrings or meaningful
> indentation?


Yes, it does, because of the way that definition works in Python.  Keep 
in mind that definitions are generated at *run-time*, with dependent 
suites being handled appropriately according to the type (class, def) of 
compound statement being executed.  Assignment isn't working any 
differently in class definitions than it is anywhere else; it's just 
that suites are handled slightly differently in class statements than 
they are in def statements.  (And this different behavior is essential, 
as that's what creates the difference between a class and a function.)

You're asking now that what appears to be a single suite is actually two 
separate entities, even though there's no visual indication of the 
break-point (except for the presence of "magic" variables).  One of 
those suites is executed when the def statement is; the other is 
executed when the function object is called.  Wildly different semantics 
from very similar-looking code at the same level of indentation, based 
on what *looks* to anyone familiar with current Python as if it's merely 
an odd naming convention.

(I'm sure that you'll argue that the presence of those "magic" variables 
is enough distinction between the two radically-different blocks of 
code; I'm also pretty confident that very few people will agree with 
you, and that nobody with a reasonable understanding of Python internals 
will be among those few people.)

Jeff Shannon
Technician/Programmer
Credit International