Yield from coroutine vs yield from task

Question

Guido van Rossum, in his speech in 2014 on Tulip/Asyncio shows the slide:

Tasks vs coroutines

• Compare:

Answer 1

As described in PEP 380, the accepted PEP document that introduced yield from, the expression res = yield from f() comes from the idea of the following loop:

for res in f():
    yield res

With this, things become very clear: if f() is some_coroutine(), then the coroutine is executed. On the other hand, if f() is Task(some_coroutine()), Task.__init__ is executed instead. some_coroutine() is not executed, only the newly created generator is passed as the first argument to Task.__init__.

Conclusion:

• res = yield from some_coroutine() => coroutine continues execution and returns the next value
• res = yield from Task(some_coroutine()) => a new task is created, which stores a non-executed some_coroutine() generator object.