[Python-Dev] statically nested scopes

[M.-A. Lemburg]

Guido van Rossum wrote:
> 
> > > > To be honest, I don't think static nested scopes buy us all that
> > > > much. You can do the same now, by using keyword arguments which
> > > > isn't all that nice, but works great and makes the scope clearly
> > > > visible.
> > >
> > > Yes.  It's a hack that gets employed over and over.  And it has
> > > certain problems.  We added 'import as' to get rid of a common
> > > practice that was perceived unclean.  Maybe we should support nested
> > > scopes to get rid of another unclean common practice?
> >
> > I think the common practice mainly comes from the fact,
> > that by making globals locals which can benefit from LOAD_FAST
> > you get a noticable performance boost.
> >
> > So the "right" solution to these weird looking hacks would
> > be to come up with a smart way by which the Python compiler
> > itself can do the localizing.
> 
> Can you elaborate?  I dun't understand what you are proposing here.

See my other post... I would like to have the compiler do the
localization for me in case it sees a global which has been
"defined" static.

> > Nested scopes won't help eliminating the current keyword
> > practice.
> 
> Why not?  I'd say that
> 
>     def create_adder(n):
>         def adder(x, n=n): return x+n
>         return adder
> 
> is a hack and that nested scopes can fix this by allowing you to write
> 
>     def create_adder(n):
>         def adder(x): return x+n
>         return adder
> 
> like one would expect.  (Don't tell me that it isn't a FAQ why this
> doesn't work!)

I know... still, I consider function definitions within a
function bad style. Maybe just me, though ;-)
 
> > > I'm not saying that we definitely should add this to 2.1 (there's
> > > enough on our plate already) but we should at least consider it, and
> > > now that we have cycle GC, the major argument against it (that it
> > > causes cycles) is gone...
> >
> > Hmm, so far the only argument for changing Python lookups
> > was to allow writing lambdas without keyword hacks. Does this
> > really warrant breaking code ?
> >
> > What other advantages would statically nested scopes have ?
> 
> Doing what's proper.  Nested scopes are not a bad idea.  They weren't
> implemented because they were hard to get right (perhaps impossible
> without creating cycles), and I was okay with that because I didn't
> like them; but I've been convinced that examples like the second
> create_adder() above should reall work.  Just like float+int works
> (in Python 0.1, this was a type-error -- you had to case the int arg
> to a float to get a float result).

Ok, but how does nested scoping mix with class definitions
and global lookups then ?

-- 
Marc-Andre Lemburg
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