[Tutor] flyweight pattern using Mixin vs. Inheritance

[Alan Gauld]

"Serdar Tumgoren" <zstumgoren at gmail.com> wrote

> Given those requirements, is the Mixin approach the way to go? Either
> way, have I implemented these correctly?

I haven't looked at your code but you could use a mixin here
however I find using mixins for insantiation can bend your brain. 
I tend to use them for instance behavioural type things
.
Instead I would actually use a dictionary class attribute (see the thread 
on class attributes/methods)

The way I'd do it would be to store a dictionary of object instances 
(using some kind of unique name/id as key). In the constructor of 
each class (ie __new__()  not  __init__() check to see if the ID exists
in the dictionary and return the object if it does. Otherwise 
continue as usual.

Something like this(untested pseudo code):

class A
    instances = {}
    def __new__(self, ID, *args, **kwargs):
          if ID in instances:
             return ID
    def __init__(self, *args, **kwargs):
          if ID in self.instances:
                return
          else:
                # init as usual.
    def __del__(self):
          del( self.instances[self.ID] )


The __del__ can probably be implemented in the top level class
and inherited.

HTH,


-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/