Nested scopes, and augmented assignment

[Diez B. Roggisch]

Tim N. van der Leeuw wrote:

> Hi,
> 
> The following might be documented somewhere, but it hit me unexpectedly
> and I couldn't exactly find this in the manual either.
> 
> Problem is, that I cannot use augmented assignment operators in a
> nested scope, on variables from the outer scope:

<snip/>

> Is this an implementation artifact, bug, or should it really just
> follow logically from the language definition?

>From the docs:

"""
An augmented assignment expression like x += 1 can be rewritten as x = x + 1
to achieve a similar, but not exactly equal effect. In the augmented
version, x is only evaluated once. Also, when possible, the actual
operation is performed in-place, meaning that rather than creating a new
object and assigning that to the target, the old object is modified
instead. 
"""

The first part is the important one. If you expand

x += 1

to 

x = x + 1

it becomes clear under the python scoping rules that x is being treated as a
local to the inner scope.

There has been a discussion about this recently on  python-dev[1] and this
NG - google for it.



Regards,

Diez


[1] http://mail.python.org/pipermail/python-dev/2006-June/065902.html