A value is missing in my iterator and I don't know why

Question

I've got a very basic generator where you can send during the loop a new value through the yield callback:

def GenInter(x, y):

    while (x+1 < y):
        callback = (yield x)
        if callback is not None:
            x = callback
        else:
            x += 1

Then, I create a generator:

myGen = GenInter(10,25)

And finally, I'm parsing it with a for loop. When it's "15", I want to go directly to "20".

for x in myGen:
    if x == 15:
        myGen.send(20)
    print(x)

Here is the result:

10
11
12
13
14
15
21
22
23

How come the "20" value is missing?

Thank you for your help.

Answer 1

The problem is that the send call actually runs an iteration and returns a value and you aren't doing anything with it.

Try this:

print(myGen.send(20))

https://repl.it/repls/RuddyConcretePrinters

Answer 2

As pointed out by @Imreal and by @Abarnert, myGen.send(20) yields the missing 20. You can resolve your issue by changing your iteration to this:

for x in myGen:
    y = x
    if x == 15:
        y = myGen.send(20)
    print(y)

It returns the following output:

10
11
12
13
14
20
21
22
23