[Python-ideas] Changing semantics of for-loop variable

[Jason Orendorff]

On Tue, Oct 4, 2011 at 7:22 AM, Ronald Oussoren <ronaldoussoren at mac.com> wrote:
> What worries me with this proposal is that it only affects the loop variable, and not other variables.

Right. Another similar example:

    def f1(seq):
        for i in seq:
            yield lambda: i.name    # each lambda refers to a different i

    def f2(seq):
        for i in seq:
            x = i.name
            yield lambda: x    # each lambda refers to the same local x

Think of f2 as a refactoring of f1. I think the programmer has a right
to expect that to work, but it would change behavior in a really
surprising way.

Also: What if the loop variable is also used elsewhere in the function?

    def f(seq):
        i = None
        for i in seq:
            pass
        return i

Does the loop variable get a cell in this case? If so, I guess it must
be a different variable from the local i. So would f([1]) return None?
That would be a rather astonishing change in behavior!

So perhaps the loop variable cell would be kept in sync with the local
variable during the loop body? It all seems too weird.

-j