Python 2 namespace change? (was Re: [Python-Dev] Changing existing class instances)

[Jim Fulton]

Jim Fulton wrote:
> 
> Reloading a module redefines the global variables in a module.
> It doesn't update any references to those global references
> from other places, such as instances or *other* modules.
> 
> For example, imports like:
> 
>   from foo import spam
> 
> are not updated when foo is reloaded.

A change to the way that namespaces are handled 
could make this work and have a number of other benefits, 
like global name usage without namespace lookups.

I've suggested this to Guido in the past.  His 
reasonable response is that this would be too big a 
change for Python 1. Maybe this is something to consider
for Python 2?

The basic idea (borrowed from Smalltalk) is to have a kind 
of dictionary that is a collection of "association" 
objects.  An association object is simply a pairing of a 
name with a value. Association objects can be shared among 
multiple namespaces.  An import like:

  from foo import spam

would copy the association between the name 'foo' and a 
value from module 'spam' into the current module. If foo
is reloaded or if the name is reassigned in spam, the
association is modified and the change is seen in any
namespaces that imported foo.

Similarly if a function uses a global variable:

  spam=1

  def bar():
    global spam
    return spam*2

the compiled function contains the association between
spam and it's value. This means that:

  - When spam is used in the function, it doesn't have to
    be looked up,

  - The function object no longer needs to keep a reference
    to it's globals. This eliminates an annoying circular 
    reference.

(I would not replace existing dictionaries with this new kind.
 I'd have both kinds available.)

I think that this would be a really nice change for Python 2.

Jim

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