[Python-Dev] violently deprecating exec without in (was: nested scopes. global: have I got it right?)

[Jeremy Hylton]

>>>>> "GvR" == Guido van Rossum <guido@digicool.com> writes:

  >> >   SP> # top-level
  >> >   SP> def g():
  >> >   SP>   exec "x=3" return x

  GvR> [me]
  >> Unfortunately this used to work, using a gross hack: when an exec
  >> (or import *) was present inside a function, the namespace
  >> semantics *for that function* was changed to the pre-0.9.1
  >> semantics, where all names are looked up *at run time* first in
  >> the locals then in the globals and then in the builtins.
  >>
  >> I don't know how common this is -- it's pretty fragile.  If
  >> there's a great clamor, we can put this behavior back after b1 is
  >> released.

  GvR> I spoke too soon.  It just works in the latest 2.1b1.  Or am I
  GvR> missing something?

The nested scopes rules don't kick in until you've got one function
nested in another.  The top-level namespace is treated differently
that other function namespaces.  If a function is defined at the
top-level then all its free variables are globals.  As a result, the
old rules still apply.

Since class scopes are ignored for nesting, methods defined in
top-level classes are handled the same way.

I'm not completely sure this makes sense, although it limits code
breakage; most functions are defined at the top-level or in classes!
I think it is fairly clear, though.

Jeremy