> >> > 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.
This doesn't make sense. If the free variables were truely considered
globals, the reference to x would raise a NameError, because the exec
doesn't define it at the global level -- it defines it at the local
level. So apparently you are generating LOAD_NAME instead of
LOAD_GLOBAL for free variables in toplevel functions. Oh well, this
does the job!
> 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.
Yeah, it's pretty unlikely that there will be much code breakage of
this form:
def f():
def g():
exec "x = 1"
return x
(Hm, trying this I see that it generates a warning, but with the wrong
filename. I'll see if I can use symtable_warn() here.)
--Guido van Rossum (home page: http://www.python.org/~guido/)
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