Getting around Python recursion limit

recursive_call.py

# https://speakerdeck.com/dabeaz/generators-the-final-frontier?slide=163
def cps(gen):
    stack = [gen]
    ret = None
    while stack:
        try:
            value, ret = ret, None
            res = stack[-1].send(value)
            stack.append(res)
        except StopIteration as e:
            stack.pop()
            ret = e.value
    return ret

def factorial(n):
    if n <= 1:
        return 1
    value = factorial(n - 1)
    return value * n

#print(factorial(1000))

def factorial(n):
    if n <= 1:
        return 1
    value = yield factorial(n - 1)
    return value * n

print(cps(factorial(10000)))

def countdown(start):
    print start
    if start == 0:
        return 0
    else:
        return countdown(start - 1)

print(cps(countdown(1000)))