"+=" does not work correct all alogn

[Olive]

On Wed, 18 Jan 2012 09:52:55 +0000 (GMT)
Wilfried Falk <w_h_falk at yahoo.de> wrote:

> Hello Pythons,
>  
> attached to this email is a pdf-file which shows, that  "+=" does not
> work well all along. Mybe somebody of you is able to explain my
> observations in this respect. I will be glad about an answer. Best
> regards Wilfried

I am not sure I understand your first question. For the second this is
explained here:
http://docs.python.org/tutorial/controlflow.html#default-argument-values

In the first case, you create a new list from the empty list at each
call. In the second case, you modify the argument in place and it is
not reevaluated between calls.

Olive