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generators as decorators simple issue

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  generators as decorators simple issue j.m.dagenhart@gmail.com - 2012-09-11 19:28 -0700
    Re: generators as decorators simple issue Ramchandra Apte <maniandram01@gmail.com> - 2012-09-11 19:55 -0700
    Re: generators as decorators simple issue alex23 <wuwei23@gmail.com> - 2012-09-11 21:39 -0700
    Re: generators as decorators simple issue Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-12 08:08 +0200
    Re: generators as decorators simple issue pyjoshsys <j.m.dagenhart@gmail.com> - 2012-09-12 03:22 -0700
      Re: generators as decorators simple issue Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-09-12 11:47 +0100
      Re: generators as decorators simple issue Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-12 09:09 -0600
    Re: generators as decorators simple issue pyjoshsys <j.m.dagenhart@gmail.com> - 2012-09-12 04:15 -0700

#28921 — generators as decorators simple issue

I'm trying to call SetName on an object to prevent me from ever having to call it explictly again on that object. Best explained by example.


def setname(cls):
    '''this is the proposed generator to call SetName on the object'''
    try:
        cls.SetName(cls.__name__)
    finally:
        yield cls


class Trial:
    '''class to demonstrate with'''
    def SetName(self, name):
        print 1, 1

@setname
class Test(Trial):
    '''i want SetName to be called by using setname as a decorator'''
    def __init__(self):

        print 'Yay! or Invalid.'

if __name__ == '__main__':
    test = Test()


How can i fix this? 
This is my exact error: python decors2.py 
Traceback (most recent call last):
  File "decors2.py", line 23, in <module>
    test = Test()
TypeError: 'generator' object is not callable

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#28922

On Wednesday, 12 September 2012 07:58:10 UTC+5:30, pyjoshsys  wrote:
> I'm trying to call SetName on an object to prevent me from ever having to call it explictly again on that object. Best explained by example.
>
[snip]
In your decorator, you are using `yield cls` - it should be `return cls` 99.99% of the time.

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#28928

On Sep 12, 12:28 pm, j.m.dagenh...@gmail.com wrote:
> def setname(cls):
>     '''this is the proposed generator to call SetName on the object'''
>     try:
>         cls.SetName(cls.__name__)
>     finally:
>         yield cls

A generator is (basically) a callable that acts like an iterator.
You'd use a generator if you wanted to loop with for or a list
comprehension across the output of the generator: for foo in
setname(Test)

A decorator is a callable that takes another callable as an argument,
either modifying it or returning a wrapped version of it: Test =
setname(Test)

You don't want to iterate over anything, so you should change `yield`
to `return`.

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#28931

Am 12.09.2012 04:28 schrieb j.m.dagenhart@gmail.com:
> I'm trying to call SetName on an object to prevent me from ever having to call it explictly again on that object. Best explained by example.
>
>
> def setname(cls):
>      '''this is the proposed generator to call SetName on the object'''
>      try:
>          cls.SetName(cls.__name__)
>      finally:
>          yield cls
>
>
> class Trial:
>      '''class to demonstrate with'''
>      def SetName(self, name):
>          print 1, 1
>
> @setname
> class Test(Trial):
>      '''i want SetName to be called by using setname as a decorator'''
>      def __init__(self):
>
>          print 'Yay! or Invalid.'
>
> if __name__ == '__main__':
>      test = Test()
>
>
> How can i fix this?

I am not sure what exactly you want to achieve, but I see 2 problems here:

1. Your setname operates on a class, but your SetName() is an instance 
function.

2. I don't really understand the try...finally yield stuff. As others 
already said, you probably just want to return. I don't see what a 
generator would be useful for here...

def setname(cls):
      '''this is the proposed generator to call SetName on the object'''
      try:
          cls.SetName(cls.__name__)
      finally:
          return cls

and

class Trial(object):
     '''class to demonstrate with'''
     @classmethod
     def SetName(cls, name):
         print 1, 1

should solve your problems.

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#28942

The output is still not what I want. Now runtime error free, however the output is not what I desire.



def setname(cls):
    '''this is the proposed generator to call SetName on the object'''
    
    try:
        cls.SetName(cls.__name__)
    except Exception as e:
        print e
    finally:
        return cls

class Trial(object):
    '''class to demonstrate with'''
    def __init__(self):
        object.__init__(self)
        self.name = None
    
    @classmethod
    def SetName(cls, name):
        cls.name = name

@setname
class Test(Trial):
    '''i want SetName to be called by using setname as a decorator'''
    def __init__(self):
        Trial.__init__(self)

        

if __name__ == '__main__':
    test = Test()
    print 'instance'
    print '', test.name #should be Test
    print 'class'
    print '', Test.name
    

The output is: python decors2.py 
instance
 None
class
 Test

I want: 
instance
 Test
class
 Test

Is this possible in this manner?

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#28943

On Wed, 12 Sep 2012 03:22:31 -0700 (PDT), pyjoshsys 
<j.m.dagenhart@gmail.com> wrote:
> The output is still not what I want. Now runtime error free, 
however the output is not what I desire.

> def setname(cls):
>     '''this is the proposed generator to call SetName on the 
object'''

>     try:
>         cls.SetName(cls.__name__)
>     except Exception as e:
>         print e
>     finally:
>         return cls

I would write the function above in one line:

cls.name = name


> class Trial(object):
>     '''class to demonstrate with'''
>     def __init__(self):
>         object.__init__(self)
>         self.name = None

Remove the line above. The instance attribute self.name is hiding the 
class attribute cls.name.

Oscar

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#28972

On Wed, Sep 12, 2012 at 4:22 AM, pyjoshsys <j.m.dagenhart@gmail.com> wrote:
> The output is still not what I want. Now runtime error free, however the output is not what I desire.

[SNIP]

> class Trial(object):
>     '''class to demonstrate with'''
>     def __init__(self):
>         object.__init__(self)
>         self.name = None
>
>     @classmethod
>     def SetName(cls, name):
>         cls.name = name

[SNIP]

> if __name__ == '__main__':
>     test = Test()
>     print 'instance'
>     print '', test.name #should be Test
>     print 'class'
>     print '', Test.name
>
>
> The output is: python decors2.py
> instance
>  None
> class
>  Test
>
> I want:
> instance
>  Test
> class
>  Test
>
> Is this possible in this manner?


The SetName class method sets the name on the *class* dictionary.  The
class's __init__ method also sets a name (None) on the *instance*
dictionary.  From an instance's perspective, the instance dictionary
will shadow the class dictionary.  If you remove the attribute from
the instance dictionary entirely (delete the "self.name = None" line),
and leave the class dictionary as is, then you will get the output you
want (although from your later post I am not certain that this is the
behaviour you want).


On Wed, Sep 12, 2012 at 5:15 AM, pyjoshsys <j.m.dagenhart@gmail.com> wrote:
> so decorators only pass the object and not any instance of the object as the implied argument? Is this right?

Right.

> The idea was to use @setname instead of instance.SetName(instance.__name__).

The appropriate place to do this so that it applies to all instances
of the class rather than to the class would be inside the __init__
method.

Also, instances don't have a __name__ attribute, so it's still unclear
to me what you're looking for.  Did you mean the effect to be that of
"instance.SetName(cls.__name__)"?  If so, then the decorator approach
(with the line "self.name = None" removed) should be fine for your
purposes -- you'll just have the name stored in the class dict instead
of in each instance dict, but it will still be visible as long as you
haven't shadowed it.

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#28946

so decorators only pass the object and not any instance of the object as the implied argument? Is this right?

The idea was to use @setname instead of instance.SetName(instance.__name__).

I thought decorators would do this, but it seems not.

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