from time import time
from types import GeneratorType


def bootstrap(f, stack=[]):
    def wrappedfunc(*args, **kwargs):
        if stack:
            return f(*args, **kwargs)
        else:
            to = f(*args, **kwargs)
            while True:
                if type(to) is GeneratorType:
                    stack.append(to)
                    to = next(to)
                else:
                    stack.pop()
                    if not stack:
                        break
                    to = stack[-1].send(to)
            return to

    return wrappedfunc
a = time()

@bootstrap
def fun(n):
    if n == 0:
        yield
    yield fun(n-1)
    yield


for i in range(10000):
    fun(400)
b = time()
print(b-a)
# took 0.34096312522888184 s in pypy3