class closure question

[Peter Otten]

Steven W. Orr wrote:

> I want to indirectly change the value of a variable.
> 
> #! /usr/bin/python
> foo = [44]
> bar = foo
> bar[0] = 55
> print 'bar = ', bar
> print 'foo = ', foo
> 
> This works fine.
> 
> bar =  [55]
> foo =  [55]
> 
> But I want to do the same with a class value.
> 
> #! /usr/bin/python
> S = None
> dd = { 'class': [S] }
> class C1(object):
>      def __init__(self):
>          print 'Hello from C1'
> 
> def mkclass(base):
>      class zzz(base):
>          pass
>      return zzz
> 
> dd['class'][0] = mkclass( C1 )
> print "dd['class'][0].__bases__ = ", dd['class'][0].__bases__
> print 'S = ', S
> 
> The answer is not what I want:
> 
> dd['class'][0].__bases__ =  (<class '__main__.C1'>,)
> S =  None
> 
> The goal is for S to be set to the returned class from mkclass.
> 
> Can someone help?

What you want is not possible in Python. You can modify some objects
(called "mutable") but rebinding a name has to be explicit.

Peter