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Newsgroups: comp.lang.python
Date: Sat, 7 Jul 2012 01:29:11 -0700 (PDT)
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Subject: Re: why greenlet, gevent or the stackless are needed?
From: "self.python" <howmuchistoday@gmail.com>
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Xref: csiph.com comp.lang.python:25006

r

2012=EB=85=84 7=EC=9B=94 7=EC=9D=BC =ED=86=A0=EC=9A=94=EC=9D=BC =EC=98=A4=
=ED=9B=84 4=EC=8B=9C 33=EB=B6=84 26=EC=B4=88 UTC+9, Devin Jeanpierre =EB=8B=
=98=EC=9D=98 =EB=A7=90:
> On Sat, Jul 7, 2012 at 3:09 AM, self.python <howmuchistoday@gmail.com> wr=
ote:
> > it there somthing that "yield" can't do
> > or just it is easier or powerful?
>=20
> couroutine-like generators can't give up control flow unless they are
> the top level function handled by the coroutine controller thing. For
> example, we can do this:
>=20
>   def foo():
>       while True:
>           next_value =3D (yield)
>           print next_value
>=20
> But we can't do this:
>=20
>   def yap():
>       next_value =3D (yield)
>       print next_value
>=20
>   def foo():
>       while True:
>           yap()
>=20
> If we explicitly say that "yap" can control us, via "yield from" (new
> in Python 3.3), then we can do something like the above, but this
> still requires explicit markup. In all other releases of Python, this
> is impossible.
>=20
> On the other hand, coroutines in greenlet et al can do a coroutine
> context switch at any point. The upside is that this is more flexible
> (and does something generators pre-3.3 cannot). The downside is that
> you now need locking structures to guarantee atomic interactions with
> a shared resource, whereas with generators you know that you always
> are the sole thing running, until you do a yield (and unless real
> threads or greenlet or whatever are involved, of course.)
>=20
> -- Devin

first, thanks for good answer:)
but I don't understand why the code



  def yap():=20
      next_value =3D (yield)=20
      print next_value=20

  def foo():=20
      while True:=20
          yap()=20

really do.
what is the purpose of that code?