PEP 342 misunderstanding

[metamoof@gmail.com]

So I've been reading up on all the new stuff in PEP 342, and trying to
understand its potential. So I'm starting with a few simple examples to
see if they work as expected, and find they dont.

I'm basically trying to do the following:

for x in range(10):
print x*2

but coroutine-style.

My initial try was:

>>def printrange():

.... for x in range(10):
.... x = yield x
.... print x
....

>>g = printrange()
>>for x in g:

.... g.send(x*2)
....
0
1
None
4
3
None
8
5
None
12
7
None
16
9
None

>>>

Now, I was expecting that to be 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20.

What am I missing here?

Moof

[Fredrik Lundh]

Re: PEP 342 misunderstandin g

metamoof@gmail. com wrote:

>>>def printrange():

... for x in range(10):
... x = yield x
... print x
...

>>>g = printrange()
>>>for x in g:

... g.send(x*2)
...
0
1
None
4
3
None
8
5
None
12
7
None
16
9
None
>
Now, I was expecting that to be 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20.
>
What am I missing here?

the output doesn't match your sample program; I assume you left out a
print statement or two from the second loop.

what you seem to be missing is that "next" (which is called by the
for-in loop) is basically the same thing as "send(None) ". in other
words, you end up pulling two items from the generator for each iteration.

</F>