[BangPypers] Adding mixing at run-time

[venkatakrishnan g]

I think this is a very nice approach. I disagree that that you could
decorate a class as @Place.mixin by mistake,
In fact i think the decorator actually makes it absolutely clear its
purpose. However, the Place.mixin should return
the mixin class.

 @classmethod
    def mixin(cls, mixin):
        """Decorator to add a mixin to the class runtime.
        """
        cls.__bases__ = cls.__bases__ + (mixin,)

        return mixin


This:

1. Allows the class to be mixed-in into other classes if there's need for it
2. Class decorators should return classes, else LinksMixin evaluates to None



On 9 October 2014 11:30, kracekumar ramaraju <kracethekingmaker at gmail.com>
wrote:

> On Wed, Oct 8, 2014 at 4:19 PM, Anand Chitipothu <anandology at gmail.com>
> wrote:
>
> > Hi,
> >
> > I'm working on a slightly large application and I'm trying to model it
> as a
> > some kind of plugin architecture so that it modular and I can enable or
> > take out features without lot of code changes.
> >
> > One of the issues I faced was that the wanted to add some methods to a
> > class only when a feature/plugin is enabled.
> >
> > Here is a simplified version of what I have:
> >
> > class Place(Mixable):
> >     def __init__(self, name):
> >         self.name = name
> >
> >     def get_users(self):
> >         return "users-of-{}".format(self.name)
> >
> >     def get_links(self):
> >         return "links-of-{}".format(self.name)
> >
> > There are couple of issues with this.
> >
> > 1. The logic for computing users or links doesn't really belong to this
> > file. I wanted to that in a separate module for modularity.
> >
> > 2. The Place class will become too large to manage over time.
> >
> > So, I came up with the following approach to address these issues.
> >
> > # place.py
> >
> > class Mixable(object):
> >     """Magic class to allow adding mixins to the class at run-time.
> >     """
> >     @classmethod
> >     def mixin(cls, mixin):
> >         """Decorator to add a mixin to the class runtime.
> >         """
> >         cls.__bases__ = cls.__bases__ + (mixin,)
> >
> > class Place(Mixable):
> >     def __init__(self, name):
> >         self.name = name
> >
> > # users.py
> > @Place.mixin
> > class UsersMixin(object):
> >     def get_users(self):
> >         return "users-of-{}".format(self.name)
> >
> >
> Is there any specific reason for using decorators ?
>
>
>
> > # links.py
> > @Place.mixin
> > class LinksMixin(object):
> >     def get_links(self):
> >         return "links-of-{}".format(self.name)
> >
> > p = Place('bangalore')
> > print(p.get_users())
> > print(p.get_links())
> >
> >
>
> I somehow feel this can lead to unexpected behaviour since Mixable classes
> are added at various files.
> This pattern looks like global variable argument (global variables are
> bad). Say if Idecorate Foo with @Place.mixin by mistake, behaviour of the
> Foo will be available in Place class and leads to side effect.
>
> How about
>
> #dispatcher.py
> # import all the classes
>
> def get_place_class():
>       # Check for features
>       for cls in classes:
>            Place.__bases__ = Place.__bases__ + (cls,)
>       return Place
>
>
>
> > With this I was able to split the class into 3 files and now I have
> > flexibility of deciding which features enable from a config file.
> >
> > What do you guys think of this approach?
> >
>
> My only concern base classes are added in different files and difficult to
> remember.
>
> Is this a good practice?
> > Are there any know flaws in this approach?
>
> How did you solve that issue when you faced similar situation?
> >
> >
> Did I understand the problem correctly ?
>
>
> > Anand
> > _______________________________________________
> > BangPypers mailing list
> > BangPypers at python.org
> > https://mail.python.org/mailman/listinfo/bangpypers
> >
>
>
>
> --
>
> *Thanks & Regardskracekumar"Talk is cheap, show me the code" -- Linus
> Torvaldshttp://kracekumar.com <http://kracekumar.com>*
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