Calling coroutine from coroutine in python

Question

I came across this issue today and I'm not quite certain why it works like this:

def outside():
    print 'before'
    inside()
    print 'after'
    yield 'World'

def inside():
    print 'inside'
    yield 'Hello'

for n in outside():
    print n

(Naive) expectation of output:

before
inside
Hello
after
World

Actual output:

before
after
World

Is it not possible to call a coroutine from inside a coroutine? The articles I read on coroutines and yield didn't elaborate on this issue and I'm quite lost here. Could anyone shed some light on this behaviour please? Thanks in advance!

Answer 1

It is totally possible. when you call inside() it creates a coroutine. In order to yield the result, you need to initialize the coroutine and yield from it as follows:

def outside():
     print 'before'
     for i in inside():
         yield i
     print 'after'
     yield 'World'

and the result would be as expected:

before
inside
Hello
after
World