memoizer.py

#Python 装饰器
#http://programmingbits.pythonblogs.com/27_programmingbits/archive/50_function_decorators.html
def memoize(f):
  cache = {}
  def helper(x):
      if x not in cache:            
          cache[x] = f(x)
      return cache[x]
  return helper


@memoize
def fib(n):
    if n in (0, 1):
        return n
    else:
        return fib(n - 1) + fib(n - 2)