Python becoming less Lisp-like

[Jeff Shannon]

Antoon Pardon wrote:
> Op 2005-03-16, Jeff Shannon schreef <jeffshannon at gmail.com>:
> 
>>Bruno Desthuilliers wrote:
>>
>>>- if x is a class attribute of class A and a is an instance of A, 
>>>a.x=anyvalue create a new instance attribute x instead of modifying A.x
>>
>>This is very consistent with the way that binding a name in any scope 
>>will shadow any bindings of that name in "higher" scopes.  It is the 
>>same principle by which one is able to use the same name for a 
>>function-local variable that is used for a global variable, without 
>>destroying that global variable.  [...]
> 
> Not entirely. The equivallent is imposible in function scope.
> If function scope would work exactly equivallent as the
> above the following should work 
> 
>     a = 42
>     def f():
>       a = a + 1
>       print a
>     print a
> 
> And the result should be:
> 
> 43
> 42
> 

I'd still say that the name binding rules are very consistent.  The 
name lookup rules are a little different (as they *should* be for 
class/instance attributes), and that's why there's a different net 
effect (UnboundLocalError) as shown in your example.  I'd say, 
however, that if there's a special case here it's with the 
function-local variables, not the class/instance attributes.  It's the 
optimizations to the function-local namespace which prevent 
transparent re-binding of global names.  And given that the 
function-local namespace is by far the most heavily used, and the 
relative utility (and wisdom) of using globals in this way, this is a 
case where the benefit of the special case is well worth the cost of 
its slight inconsistency.

Jeff Shannon