[Tutor] python closures

[Hugo Arts]

On Mon, Nov 30, 2009 at 4:16 PM, Kent Johnson <kent37 at tds.net> wrote:

> That has not been needed since 2.1 though it is still useful when
> closures are created in a loop (because closures are kind of late
> bound - I'm not sure the exact technical explanation):
> In [13]: def f():
>   ....:     l = []
>   ....:     for i in range(3):
>   ....:         def g():
>   ....:             print i
>   ....:         l.append(g)
>   ....:     return l
>
> In [14]: for g in f(): g()
>   ....:
> 2
> 2
> 2
>

This doesn't really have anything to do with closures specifically.
Variable lookup is done at runtime, not definition time. So when these
lookups for i are performed the value of i is indeed 2.

This wouldn't happen if closures used pointer references (as spir
called them). Then again, even with pointer references modifications
to mutable variables are still visible inside a closure.

Hugo