[Python-Dev] Re: Dynamic nested scopes

[Guido van Rossum]

[Barry, on dynamic scopes]
> This is how Emacs Lisp behaves, and it's used all the time in ELisp
> programs.  On the one hand it's quite convenient for customizing the
> behavior of functions.  On the other hand, it can make documenting the
> interface of functions quite difficult because all those dynamically
> scoped variables are now part of the function's API.
> 
> It's interesting to note that many ELispers really hate dynamic
> scoping and pine for a move toward lexical scoping.  I'm not one of
> them.

I don't care what you pine for in ELisp, but for Python this would be
a bad idea.

> I'm not as concerned about "fixing" nested functions because I hardly
> ever use them, and rarely see them much in Python code.  Fixing
> lambdas would be nice, but since Guido considers lambdas themselves a
> mistake, and given that lamda use /can/ be a performance hit in some
> situations, does it make sense to change something as fundamental as
> Python's scoping rules to fix this eddy of the language?

I referred to this in our group meeting as "fixing lambda" because
that's where others seem to need it most often.  But it is a real
problem that exists for all nested functions.  So let me rephrase
that: "fixing nested function definitions" is useful, if it can be
done without leaking memory, without breaking too much existing code,
and without slowing down code that doesn't use the feature.

--Guido van Rossum (home page: http://www.python.org/~guido/)