python - exhausted iterators - what to do about them?

Question

(In Python 3.1) (Somewhat related to another question I asked, but this question is about iterators being exhausted.)

# trying to see the ratio of the max and min element in a container c
filtered = filter(lambda x : x is not None and x != 0, c)
ratio = max(filtered) / min(filtered)

It took me half hour to realize what the problem is (the iterator returned by filter is exhausted by the time it gets to the second function call). How do I rewrite it in the most Pythonic / canonical way?

Also, what can I do to avoid bugs of this sort, besides getting more experience? (Frankly, I don't like this language feature, since these types of bugs are easy to make and hard to catch.)

Answer 1

The itertools.tee function can help here:

import itertools

f1, f2 = itertools.tee(filtered, 2)
ratio = max(f1) / min(f2)