Set the return value of a function, but return later

returnlater.py

def returnlater(f):
    def inner(*args, **kwargs):
        x = f(*args, **kwargs)
        r = None
        while True:
            try:
                r = next(x)
            except StopIteration as final:
                if final.value is not None:
                    return final.value
                return r
    return inner

@returnlater
def test(x, default=None):
    if default:
        yield default
    if x < 5:
        yield "x < 5"
    elif x < 10:
        yield "x < 10"
    if x > 100:
        return "That's too big!"

print(test(3))
print(test(8))
print(test(20))
print(test(20, "Unknown"))
print(test(1000, "Unknown"))

"""
x < 5
x < 10
None
Unknown
That's too big!
"""