User or UserManager ? Problems of Observer Pattern

[一首诗]

Thanks for your advice.

I studied python from the tutorial and the library manual, and I think
I am familiar enough with Python's grammar and API.  That's why I
never thought I need to read a book of Python.

But if "Programming Python" also explains OO, I would be happy to read
it.
In fact, I am also planning to read again "Head First Object-Oriented
Design and Analysis".
I thought it's time for me to try again to find what is the *point* of
Obejct.

Anyway, this time I will be patient enough.  I won't touch my code
until I am sure find some way to improve it.

On Apr 4, 1:14 pm, Michele Simionato <michele.simion... at gmail.com>
wrote:
> On Apr 3, 7:34 pm, 一首诗 <newpt... at gmail.com> wrote:
>
>
>
> > #----------------
> > # Choice 2
> > #----------------
>
> > class UserManager:
>
> >     users = []
>
> >     @classmethod
> >     def delUser(cls, user):
> >         cls.users.remove(user)
>
> >         RoleManager.onUserDel(user)
>
> > class RoleManager:
>
> >     roles = []
>
> >     @classmethod
> >     def onUserDel(cls, user):
> >         for r in cls.roles.items():
> >             r.users.remove(user)
>
> Choice #2 is better, but it should not be implemented
> this way. Using a class as a pure container of methods,
> a big singleton, makes little sense, since you would
> be better off with a module and old fashioned procedural
> programming. You recognize this and are worried about this.
> You do not need to be worried to much,
> since there is nothing wrong with procedural design
> (but you should use modules not classes). If you want
> to be more object oriented, the first thing is to understand
> is that you define objects in order to pass them to
> other objects. For instance, you are using a global
> list of users as a class attribute, but I would
> just pass the list in the __init__ method, and
> make it an instance attribute. I also would make
> a RoleManager instance and pass it to the UserManager,
> so that it can be used directly. Or perhaps I would
> define a single UserRoleManager doing all the job.
> It depends.
> But all the point of OOP is to pass objects to other objects.
> It is not bad to think of a data object as of a record
> on steroids. Objects which are purely data and not
> behavior are the simplest and the best objects, start
> from them.
> There are also objects which are mostly behavior
> and nearly no data (the Manager objects here, which
> just act over collections of other objects). Those
> are more difficult to write. OTOH, nobody forces you
> to write the managers as objects. You may find easier
> to write a set of manager functions. This set of
> functions can later become methods of a Manager object,
> if it seems fit, but that must be done a posteriori,
> not a priori.
> Perhaps you should read some book like "Programming Python"
> by Ludz which has many examples of how to write OO applications
> in Python (I mean no offense, but indeed from you examples
> is seems to me that you are missing the point of OOP,
> as you are the first to recognize).
> HTH,
>
>                Michele Simionato