On Aug 26, 2008, at 7:20 PM, Kent Johnson wrote:
On Tue, Aug 26, 2008 at 1:36 AM, Eric Abrahamsen
<[EMAIL PROTECTED]> wrote:
So my test case: a Month has a 'child' attribute pointing at Week,
which has
a 'child' attribute pointing at Day, so they all know what kind of
child
instances iteration should produce. With nested loops, a Month
produces one
Week, that Week produces seven Days, then the next Week is
produced, it
makes seven more Days, etc. That much is easy.
If all you want to do with the nested Month, etc is to iterate the
events in them, you could probably use a shared iterator. It would
have to be able to push-back items so that when you hit the
out-of-range item you could push it back on the iterator.
Is a 'shared iterator' something special, or do you mean all the
instances would draw their events from a single iterator? I'm not sure
what this would look like.
Then there's self.events. My original code looped over all of
self.events
for each child produced. A Month loops over its events four times,
a Week
seven times. This was the straightforward implementation, but it
seemed
inefficient. (I also, as you point out, might have been wrong about
the way
django QuerySets work). My thought was that only one loop over
self.events
should be necessary, in theory, since they're sorted by date.
Instead of direct use of the list iterator, you could pass the list
and the starting index around. Then you don't have to keep finding
your place.
That's a definite possibility, I'll try it out. Itertools.tee is also
something I've yet to look at closely. Thanks for these hints.
A for loop creates an iterator from a sequence and calls next() on
it, and
it creates an entirely new iterator each time you start a new for
loop:
I still don't understand your code but you may have another
misconception. Calling iter() on an iterator returns the same
iterator; it does not make a new iterator that holds the same place.
You can use itertools.tee() to split an iterator if that is what you
want to do.
Just for the sake of argument, here's the principle I'm working from:
#####
>>> lst = range(10)
>>> iterlst = iter(lst)
>>> iterlst.next()
0
>>> for x in iterlst:
... if x < 5:
... print x
... else:
... break
...
1
2
3
4
>>> for x in iterlst:
... print x
...
6
7
8
9
#####
So that's why I'm creating the iterator outside of the while loop in
the original code, and then using a repeated for loop with a break to
step through all the events only once. Of course, the fact that 5
isn't in there probably points to the source of my problems! The
solution might be assigning iterlist.next() to a variable, and
advancing the variable.
Thanks,
Eric
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