unintuitive for-loop behavior

[Gregory Ewing]

Steve D'Aprano wrote:

> # create a new binding
> x: address 1234 ----> [  box contains 999 ]
> x: address 5678 ----> [  a different box, containing 888 ]

In the context of CPython and nested functions, replace
"box" with "cell".

When I said "creating a new binding" I meant that the
name x refers to different cells at different times.
When I said "updating an existing binding" I meant that
the name x still refers to the same cell, but that cell
refers to a different object.

In a wider context, replace "box" with "slot in a
stack frame" or "slot in a namespace dictionary".

> But Python doesn't work that way! Variables aren't modelled by boxes in
> fixed locations, and there is no difference between "create a new binding"
> and "update an existing one".

There is very much a distintion. Each time you invoke
a function, a new set of bindings is created for all of
its parameters and local names. Assigning to those names
within the function, on the other hand, updates existing
bindings.

-- 
Greg