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Date: Tue, 2 Jul 2013 07:22:10 +0100
From: Marcin Szamotulski <mszamot@gmail.com>
To: python-list@python.org
Subject: Re: Stupid ways to spell simple code
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On 22:09 Mon 01 Jul     , Steven D'Aprano wrote:
> On Mon, 01 Jul 2013 20:36:29 +0100, Marcin Szamotulski wrote:
> 
> > Here is another example which I came across when playing with
> > generators, the first function is actually quite useful, the second
> > generator is the whole fun:
> > 
> > from functools import wraps
> > def init(func):
> >     """decorator which initialises the generator """
> >     @wraps(func)
> >     def inner(*args, **kwargs):
> >         g = func(*args, **kwargs)
> >         g.send(None)
> >         return g
> >     return inner
> > 
> > @init
> > def gen(func):
> >      x = (yield)
> >      while True:
> >          x = (yield func(x))
> > 
> > 
> > now if you have function f
> > def f(arg):
> >     return arg**2
> > 
> > then calling f(5) is the same as
> > 
> > g = gen(f)
> > g.send(5)
> 
> 
> 
> I think you must be missing an important part of the trick, because 
> calling f(5) returns 25. It's not:
> 
> @gen
> def f(arg):
>     return arg**2
> 
> 
> because that raises TypeError.
> -- 
> Steven
> -- 
> http://mail.python.org/mailman/listinfo/python-list

Sure it does,  you're now supposed to use .send method instead of
calling it but this is just different syntax.  If you want to call it
use this :

def identity(func):
    @init
    def gen(func):
        x = (yield)
        while True:
            x = (yield func(x))
    return gen(func).send

Now you will get:

>>> @identity
>>> def f(a): a+1
...
>>> f(0)
1

Best regards,
Marcin