CODEWITHSUNDEEP
pythonpython-2.7yield
James Sapam
James Sapam

Reputation: 16940

Passing value to yield using send

When i was googling for python yield i found something interesting and I never knew before i.e we can pass value to yield to change the next() value. I hope some of the new pythonist might now aware of this and I am not sure how it works too. So, If any body could explain how it works and how the behavior changes when i send a new index to yield using send().

Here is my snippets :

def print_me (count):
    i = 0
    while i < count:
        val = (yield i)
        if val is not None:
            i = val
        else:
            i += 1

gen = print_me(10)

for i in gen:
   if i == 5:
       gen.send(8)
   else:
       print i

Here is my output:

0
1
2
3
4
9

Upvotes: 3

Views: 2551

Answers (1)

mgilson
mgilson

Reputation: 310089

Your test code is pretty instructive actually. What happens in a generator function like this is that whenever you call next on the generator, code gets executed until it hits a yield statement. The value is yielded and then execution in the generator "pauses". If you .send some data to the generator, that value is returned from yield. If you don't .send anything, yield returns None.

So in your code, when you .send(8), then it sets val = 8 inside your generator (val = yield i). since val is not None, i is set to 8. .send actually executes until the next yield statement (returning that value -- 8). Then things resume as normal (the next number to be yielded is 9).

Upvotes: 4

Related Questions