cached.py

#!/bin/python
from collections import OrderedDict

def memo(f, k):
    cache = OrderedDict()
    def memoized(n):
        if n not in cache:
            cache[n] = f(n)
            if len(cache) > k:
                del cache[cache.keys()[0]]
        return cache[n]
    return memoized

def fib(n):
    print 'We are computing'
    if n == 1:
        return 0
    if n == 2:
        return 1
    return fib(n - 2) + fib(n - 1)

fib_m = memo(fib, 3)

fib_m(3)
fib_m(4)
fib_m(5)
fib_m(6)
fib_m(3)
fib_m(4)