> [Guido]
> > [Jeremy and Tim argue about what to do about write access for
> > variables at intermediate levels of nesting, neither local nor
> > module-global.]
> >
> > I'll risk doing a pronouncement, even though I know that Jeremy (and
> > maybe also Tim?) disagree.
> >
> > You don't need "write access" (in the sense of being able to assign)
> > for variables at the intermediate scopes, so there is no need for a
> > syntax to express this.
[Tim]
> I can live with that! Reference-only access to intermediate scopes would
> address 99% of current gripes. Of course, future gripes will shift to that
> there's no rebinding access. If we have to support that someday too, my
> preferred way of spelling it in Python requires explicit new syntax, so
> adding that later would not break anything.
Exactly my point.
> > Assignments are to local variables (normally) or to module-globals (when
> > 'global' is used). Use references search for a local, then for a local of
> > the containing function definition, then for a local in its container,
>
> The Pascal standard coined "closest-containing scope" to describe this
> succinctly, and I recommend it for clarity and brevity.
Thanks, that's a good term. And the principle is totally
uncontroversial.
> > and so forth, until it hits the module globals, and then finally it looks
> > for a builtin.
> >
> > We can argue over which part of this is done statically and which part
> > is done dynamically: currently, locals are done dynamically and
> > everything else is done statically.
>
> I'm not sure what you're trying to say there, but to the extent that I think
> I grasp it, I believe it's backwards: locals are static today but
> everything else is dynamic (and not in the sense of "dynamic scoping", but
> in the operational sense of "requires runtime search to resolve non-local
> names", while local names are fully resolved at compile-time today (but in
> the absence of "exec" and "import *")).
Oops, yes, I had it backwards.
As I said elsewhere, in Python 3000 I'd like to do it all more
statically. So perhaps we should look up nested locals based on
static information too. Thus:
x = "global-x"
def foo():
if 0:
x = "x-in-foo"
def bar():
return x
return bar
print foo()()
should raise UnboundLocalError, not print "global-x".
--Guido van Rossum (home page: http://www.python.org/~guido/)
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