I am trying to learn how generators work and part of that is the `send()` command that allows me to change the operation of the generator by sending back information to the generator.

I have a very simple example in which I am sending back the yielded value and add it to an internal `status`. 
The generator can be started specifying the number of values it is supposed to yield.

The incredibly strange thing is: When I start the generator with an even number it works, however if I ask to yield an odd number of values I get an `StopIteration` error.


To debug, I added a simple `print()` to keep track of how many iterations it goes through and it seems like it does two iterations per `yield` statement, which makes no sense to me.

The Code:
```
def jump_ahead(length):
    """
    generator that jumps ahead
    """
    status = 1
    iteration = 0
    while iteration < length:
        iteration += 1
        print("iteration: ", iteration)
        result = (yield status)
        if result is not None:
            status += result


if __name__ == "__main__":
    # simple generator that expects a value back
    # this works
    jumpy = jump_ahead(4)
    for i in jumpy:
        jumpy.send(i)
        print(i)
    # this does not
    jumpy_fail = jump_ahead(5)
    for i in jumpy_fail:
        jumpy_fail.send(i)
        print(i)
```

The output looks something like this
``` 
iteration:  1
iteration:  2
1
iteration:  3
iteration:  4
2
iteration:  1
iteration:  2
1
iteration:  3
iteration:  4
2
iteration:  5
  (...) StopIteration
```