associated to my blog: http://matsub.hatenablog.com/entry/2015/01/30/185724

memoize.py

#!/usr/bin/env python3
# codin: utf-8


# memoizing decorator
def memoize(function):
    def _memoize(*args, _cache={}):
        if args in _cache:
            print('return using cached')  # just for logging
            return _cache[args]
        result = function(*args)
        _cache[args] = result
        print('memoized', args)  # jsut for logging
        return result
    return _memoize


if __name__ == '__main__':
    # compute modular exponentiation
    @memoize
    def pmod(base, exponent, mod):
        n = 1
        while exponent:
            if exponent & 1:
                n = (n*base) % mod
            exponent >>= 1
            base = (base**2) % mod
        return n

    # determine n is a probable prime or not
    @memoize
    def is_pseudoprime(n):
        industrial_grade = (2, 3, 5, 7)
        if n in industrial_grade:
            return True
        for base in industrial_grade:
            if pmod(base, n-1, n) != 1:
                return False
        return True

    # confirm that the cache has goodbye on another decorated
    @memoize
    def square(n):
        return n**2

    print('>>> is 2 a prime number?')
    print(is_pseudoprime(2))
    print('>>> really?')
    print(is_pseudoprime(2))
    print('>>> okay then, the square of 2 is what?')
    print(square(2))