yield expression

Newsgroups	comp.lang.python
Date	2013-02-24 16:36 -0800
Message-ID	<d7760f61-08dd-4186-8844-5f8415773a49@googlegroups.com> (permalink)
Subject	yield expression
From	Ziliang Chen <zlchen.ken@gmail.com>

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Hi folks,
When I am trying to understand "yield" expression in Python2.6, I did the following coding. I have difficulty understanding why "val" will be "None" ? What's happening under the hood? It seems to me very time the counter resumes to execute, it will assign "count" to "val", so "val" should NOT be "None" all the time.

Thanks !

code snippet:
----
 def counter(start_at=0):
     count = start_at
     while True:
         val = (yield count)
         if val is not None:
             count = val
         else:
             print 'val is None'
             count += 1

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yield expression Ziliang Chen <zlchen.ken@gmail.com> - 2013-02-24 16:36 -0800
  Re: yield expression "Colin J. Williams" <cjw@ncf.ca> - 2013-02-26 11:34 -0500
    Re: yield expression Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-26 09:50 -0700
    Re: yield expression Dave Angel <davea@davea.name> - 2013-02-26 12:05 -0500
    Re: yield expression "Vytas D." <vytasd2013@gmail.com> - 2013-02-26 17:07 +0000
      Re: yield expression "Colin J. Williams" <cjw@ncf.ca> - 2013-02-26 13:44 -0500
        Re: yield expression Dave Angel <davea@davea.name> - 2013-02-26 21:59 -0500
      Re: yield expression "Colin J. Williams" <cjw@ncf.ca> - 2013-02-26 13:44 -0500

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