Python Help!!! I have a function that that returns the nth number in a fibonacci sequence.

Here is the function:

def fib(n): if n == 0: return 0 elif n == 1: return 1 else: return fib(n-1)+fib(n-2)

Write a function mfib(n) that uses memoization to greatly speed up the calculation. Use a dictionary to memoize each value of fib(n) as they are computed.

So I now need to write a function using a dictionary to speed up the function.