Global module variables as default parameters

[Christoph Haas]

Thanks to all who answered.

On Friday 22 September 2006 17:28, Marc 'BlackJack' Rintsch wrote:
> Christoph Haas wrote:
> > TestModule.py
> > ----------------------------------------
> > globalvar = 0
> >
> > def def1():
> >   print globalvar
> >
> > def def2(foo=globalvar):
> >   print foo
> > ----------------------------------------
> >
> > Running the test.py script prints "123" and "0". So accessing the
> > globalvar in def1() works. But if I try to use the global variable as
> > a default parameter in def2() it uses the default "0". What is the
> > difference between these two? Are there contexts of default
> > parameters?
>
> Default parameters are evaluated *once* when the ``def`` is executed. 
> So in `def2` the value of `foo` won't be looked up when calling the
> function as it is already bound to the value 0.

Now that you point me to it it's pretty obvious indeed. I always forget 
that the 'def's are executed at load time, too.

Peter/John: in fact I already used a sentinel like you proposed as 
a "workaround". So there is just one sensible way to do it. Again.

Kindly
 Christoph