I working through Luciano's Fluent Python, which I really appreciate reading in Safari On-Line as so many of the links are live and relevant. Luciano packs his 'For Further Reading' with links directly in Google groups, where we can see Guido studying Twisted so to better communicate his alternative vision in asyncio (formerly tulip). Here's a tiny test module I'm using, based on Gregory Ewing's PEP 380. https://www.python.org/dev/peps/pep-0380/ from itertools import takewhile def fibo(a,b): "Fibonacci Numbers with any seed" while True: yield a a, b = a + b, a def pep380(EXPR): _i = iter(EXPR) try: _y = next(_i) except StopIteration as _e: _r = _e.value else: while 1: try: _s = yield _y except GeneratorExit as _e: try: _m = _i.close except AttributeError: pass else: _m() raise _e except BaseException as _e: _x = sys.exc_info() try: _m = _i.throw except AttributeError: raise _e else: try: _y = _m(*_x) except StopIteration as _e: _r = _e.value break else: try: if _s is None: _y = next(_i) else: _y = _i.send(_s) except StopIteration as _e: _r = _e.value break return _r def get_em(): # fibs = fibo(0,1) # yield from fibs # delegates to subgenerator # return fibs return pep380(fibo(0,1)) g = get_em() print(tuple(takewhile(lambda n: n < 1000, g))) Console output: (0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987) Now if I comment out differently: def get_em(): fibs = fibo(0,1) yield from fibs # delegates to subgenerator # return fibs # return pep380(fibo(0,1)) Same answer: (0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987) One may also return fibs directly from get_em, showing that 'yield from' is driving the same process i.e. delegation is happening. Just scratching the (itchy) surface. Kirby