Re: [Modeling-users] specifying objects' class

[Sebastien B. <sbi...@us...>]

John Lenton <jo...@vi...> wrote:
> On Tue, Feb 10, 2004 at 04:28:22PM +0100, Sebastien Bigaret wrote:
> > [...]
> >   rather you want:
> >=20
> >     Employee <|-- EmployeeBase <|-- Person <|-- PersonBase
> >=20
> >   so that Employee inherits from the business-logic defined in Person,
> >   as expected.
>=20
> hmm... it isn't clear to me that this is always what you want;
> currently we're using (in an unrelated field) a linearization of that
> graph into
>=20
>     Employee <| Person <| EmployeeBase <| PersonBase
>=20
> although I can see that in this case you are (on first sight at least)
> correct. However, no matter what is expected, it is exactly what the
> C3 MRO in python 2.3 does. If you want your behaviour, all you have to
> do is declare Employee as
>=20
>     class Employee(EmployeeBase, Person)
>=20
> whereas if you want the other behaviour you declare it as
>=20
>     class Employee(Person, EmployeeBase)
>=20
> unfortunately this only applies to new style classes as of python 2.3;
> I'm not certain the (hackish) MRO in 2.2 DWIMs.

Fine, no problem! I only wanted to point out the fact that Employee
should inherit from both EmployeeBase and Person (and additionally, the
generated code works for py2.1, 2.2 and 2.3, so I used strict
single-inheritance).


> new-style classes would be nice for several reasons, not only
> performance. For starters, the fact that you can query the MRO and use
> super(), makes multiple inheritance manageable.
>=20
> By the way, did you compare the speed of your metaclass approach to an
> exec?

  Sorry, I'm afraid I do not understand what "comparing to an exec"
  means, could you be more explicit?

-- S=E9bastien.