[Tutor] Strange modulus problem

Michael P. Reilly arcege@speakeasy.net
Sat, 13 Oct 2001 12:39:33 -0400

On Sat, Oct 13, 2001 at 11:24:27AM -0500, Chris Keelan wrote:
> On Thu, 11 Oct 2001, Kirby Urner wrote:
> > This has to do with iterating over the object you're
> > also modifying.
> When you explain it that way, it makes perfect sense! For some reason I 
> didn't think that the 'for' iteration worked by index. Perhaps there was a 
> little gnome who took all of the objects out of a list, laid them out on a 
> table and picked them up, one-by-one saying "If I divide six by this, will my 
> remainder be zero? Nope? Well throw it out then."

Also, instead of removing items, you can append items to a new list:

m = range(100)
l = []
for i in m:
  if (i % 13) == 0:
    l.append( i )

print l
[0, 13, 26, 39, 52, 65, 78, 91]

Then there is no need to create a copy of the list, which could be
expensive if the list is large, and not removing items from a list,
which you can see is problematic.


| Michael P. Reilly                | arcege@speakeasy.net              |