Understanding this generator function

[Hussein B]

Hey,
This is an example of a generator function:
=====
def counter(start_a t=0):
count = start_at
while True:
val = (yield count)
if val is not None:
count = val
else:
count += 1
======

>>count = counter(5)
>>count.next( )

5

>>count.send( 9)

9
======
I'm not able to understand how this generator function is working,
would you please me (what happens when calling next/send)?
Thanks.

[Ben Finney]

Re: Understanding this generator function

Hussein B <hubaghdadi@gma il.comwrites:

This is an example of a generator function [using coroutine
behaviour]:

[…]

I'm not able to understand how this generator function is working,
would you please me (what happens when calling next/send)?

The behaviour you're seeing was introduced in PEP 342, "Coroutines via
Enhanced Generators" <URL:http://www.python.org/dev/peps/pep-0342>,
which documents the behaviour.

Read that PEP, experiment further, and then ask any questions that you
still have after that.

--
\ “Patience, n. A minor form of despair, disguised as a virtue.” |
`\ —Ambrose Bierce, _The Devil's Dictionary_, 1906 |
_o__) |
Ben Finney

[James Mills]

Re: Understanding this generator function

Hi,

There is a great set of slides on this topic
available here: http://www.dabeaz.com/generators/

They explain this concept quite well and
walk you through everything you need to
know about generators and how powerful
they can be.

Please read it.

cheers
James

On 8/27/08, Hussein B <hubaghdadi@gma il.comwrote:

Hey,
This is an example of a generator function:
=====
def counter(start_a t=0):
count = start_at
while True:
val = (yield count)
if val is not None:
count = val
else:
count += 1
======

>>count = counter(5)
>>count.next( )

5

>>count.send( 9)

9
======
I'm not able to understand how this generator function is working,
would you please me (what happens when calling next/send)?
Thanks.
>
--

http://mail.python.org/mailman/listinfo/python-list

>

--
--
-- "Problems are solved by method"

[Jeff]

Re: Understanding this generator function

def counter(start_a t=0):

    count = start_at
    while True:
        val = (yield count)

A generator can accept a value from the consumer. So, If I have a
counter:

c = counter()

I can send it a value:

c.send(9)

        if val is not None:
            count = val

The generator tests to see it it received anything, and if it does,
resets count to what it received (in this case, 9).

        else:
            count += 1

Otherwise, it just increments count on each call.