[Python-Dev] PEP for Better Control of Nested Lexical Scopes

Brendan Simons spam4bsimons at yahoo.ca
Thu Feb 23 03:46:09 CET 2006

On 22-Feb-06, at 9:28 PM, python-dev-request at python.org wrote:

> On 21-Feb-06, at 11:21 AM, Almann T. Goo" <almann.goo at gmail.com>
>  wrote:
>>> Why not just use a class?
>>> def incgen(start=0, inc=1) :
>>>     class incrementer(object):
>>>       a = start - inc
>>>       def __call__(self):
>>>          self.a += inc
>>>          return self.a
>>>     return incrementer()
>>> a = incgen(7, 5)
>>> for n in range(10):
>>>     print a(),
>> Because I think that this is a workaround for a concept that the
>> language doesn't support elegantly with its lexically nested scopes.
>> IMO, you are emulating name rebinding in a closure by creating an
>> object to encapsulate the name you want to rebind--you don't need  
>> this
>> workaround if you only need to access free variables in an enclosing
>> scope.  I provided a "lighter" example that didn't need a callable
>> object but could use any mutable such as a list.
>> This kind of workaround is needed as soon as you want to re-bind a
>> parent scope's name, except in the case when the parent scope is the
>> global scope (since there is the "global" keyword to handle this).
>> It's this dichotomy that concerns me, since it seems to be against  
>> the
>> elegance of Python--at least in my opinion.
>> It seems artificially limiting that enclosing scope name rebinds are
>> not provided for by the language especially since the behavior with
>> the global scope is not so.  In a nutshell I am proposing a solution
>> to make nested lexical scopes to be orthogonal with the global scope
>> and removing a "wart," as Jeremy put it, in the language.
>> -Almann
>> --
>> Almann T. Goo
>> almann.goo at gmail.com
> If I may be so bold, couldn't this be addressed by introducing a  
> "rebinding" operator?  So the ' = ' operator would continue to  
> create a new name in the current scope, and the (say) ' := '  
> operator would for an existing name to rebind.   The two operators  
> would highlight the special way Python handles variable / name  
> assignment, which many newbies miss.
> (from someone who was surprised by this quirk of Python before:   
> http://www.thescripts.com/forum/thread43418.html)
>   -Brendan
> --
> Brendan Simons

Sorry, this got hung up in my email outbox.  I see the thread has  
touched on this idea in the meantime.  So, yeah.  Go team.

Brendan Simons

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.python.org/pipermail/python-dev/attachments/20060222/16807fe6/attachment.html 

More information about the Python-Dev mailing list