[Python-Dev] Re: closure semantics

[Skip Montanaro]

    >> 'global' vars [ 'in' named_scope ]
    >> 
    >> where named_scope can only be the name of a function which encloses
    >> the function containing the declaration.

    Guido> That was my first suggestion earlier this week.  The main
    Guido> downside (except from propagating 'global' :-) is that if you
    Guido> rename the function defining the scope you have to fix all global
    Guido> statements referring to it.

Well, the listed variables are "global" to the current local scope.  I find
the rename argument a bit specious.  If I rename a function I have to change
all the references to it today.  This is just one more.  Since "global" is a
declarative statement, the compiler can tell you immediately that it can't
find the old function name.

    Guido> I saw a variant where the syntax was

    Guido>     'global' vars 'in' 'def'

    Guido> which solves that concern (though not particularly elegantly).

I don't see how that can work though.  What does 'def' mean in this case?
There can be multiple lexically enclosing functions, any of which have the
same local variable x which you might want modify.

    >> This should be compatible with existing usage.  The only problem I
    >> see is whether the named_scope needs to be known at compile time or
    >> if it can be deferred until run time.

    Guido> Definitely compile time.  'f' has to be a name of a lexically
    Guido> enclosing 'def'; it's not an expression.  The compiler nees to
    Guido> know which scope it refers to so it can turn the correct variable
    Guido> into a cell.

Okay, that was easily settled. ;-)

Skip