gistfile1.py

import random
import timeit

def inter_reduce(sets):
    return reduce(set.intersection, sets)

def inter_for(sets):
    sets = iter(sets)
    result = next(sets)
    for s in sets:
        result.intersection_update(s)
    return result

random.seed(42)
sets = [set(random.randrange(1000) for i in range(4000))
        for j in range(100)]
print timeit.timeit("inter_reduce(sets)",
                    "from __main__ import inter_reduce, sets", number=1000)
print timeit.timeit("inter_for(sets)",
                    "from __main__ import inter_for, sets", number=1000)

Very nice, one thing to note about this version though is that it does modify the 1st element of the list (the function is not referentially transparent). Print out the value of sets[0] before and after the call to inter_for. Easy enough to fix, just a thought.

^^ as an addendum to this, my fork has versions that are referentially transparent, but this definitely adds significant overhead (still cheaper than reduce though). I'm pretty sure there's a better way of doing it as well.