Minimally invasive function for heap recursion

heap_rec.py

def heap_rec(f):
    stack = [f]
    result = None
    while stack:
        try:
            stack.append(stack[-1].send(result))
            result = None
        except StopIteration as ex:
            result = ex.value
            stack.pop()
    return result

def fib(n):
    if n < 2: return n
    return (yield fib(n-1)) + (yield fib(n-2))

print(heap_rec(fib(20)))