Astan Chee <stanc at al.com.au> writes on Sat, 19 Aug 2006 03:34:26 +1000:
> >>> for p in ps:
> if p in qs:
> ps.remove(p)
You are modifying an object ("ps") while you iterate over it.
This is a receipe for surprises...
The standard idiom is to iterate over a copy rather than the object itself:
for p in ps[:]:
....
Dieter