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[Ben Cartwright]

kpp9c wrote:
> I've been looking at some of the suggested approaches and looked a
> little at Michael's bit which works well.... bisect is a module i
> always struggle with (hee hee)
>
> I am intrigued by Ben's solution and Ben's distilled my problem quite
> nicely

Thanks!-)  Actually, you should use Michael's solution, not mine.  It
uses the same concept, but it finds the correct subinterval in O(log n)
steps (by using bisect on a cached list of cumulative sums).  My code
takes O(n) steps -- this is a big difference when you're dealing with
thousands of items.

> but, well....i don't understand what "point" is doing with
> wieght for key, weight for zlist

This line:
    point = random.uniform(0, sum(weight for key, weight in zlist))
Is shorthand for:
    total = 0
    for key, weight in zlist:
        total += weight
    point = random.uniform(0, total)

> furthermore, it barfs in my
> interpreter... (Python 2.3)

Oops, that's because it uses generator expressions
(http://www.python.org/peps/pep-0289.html), a 2.4 feature.  Try
rewriting it longhand (see above).  The second line of the test code
will have to be changed too, i.e.:
  >>> counts = dict([(key, 0) for key, weight in data])

--Ben