[Tutor] Calling super classs __init__?

[Andreas Kostyrka]

Am Mittwoch, den 19.03.2008, 10:36 -0300 schrieb Ricardo Aráoz:
> Luciano Ramalho wrote:
> > Nowadays the best practice for invoking a method from all superclasses
> > (yes, multiple inheritance) is this:
> > 
> > class SubClass(BaseClass):
> >     def __init__(self, t, *args, **kw):
> >         super(SubClass, self).__init__(*args, **kw)
> >         # do something with t
> > 
> > That way you let Python decide which superclasses your SubClass has,
> > instead of hard-coding it in several places.
> > 
> 
> You are actually hard-coding it here too, "class SubClass(BaseClass):" 
> has "BaseClass" hard-coded. All you do here is hard-code it once instead 
> of twice.

Yes and no. Yes a human has specified the relationships. But you do not
have to specify what other baseclasses your class has. This is relevant
for multiple inheritence, like:

D => B => A
D => C => A

The problem is mostly hiding implementation details.

Using super, you just let Python pick the "next" class to give control.
Using B.__init__ and C.__init__, A.__init__ would be called twice.

Andreas

> 
> > Cheers,
> > 
> > Luciano
> > 
> > 
> > On Tue, Mar 18, 2008 at 9:37 PM, John Fouhy <john at fouhy.net> wrote:
> >> On 19/03/2008, Allen Fowler <allen.fowler at yahoo.com> wrote:
> >>  >  I have a super class that accepts many arguments to it's constructor, and a subclass that should define one additional argument.
> >>  >
> >>  >  What's the most "pythonic" way to make this work?
> >>
> >>  class BaseClass(object):
> >>   def __init__(self, x, y, z, foo='foo'): # whatever
> >>      # etc
> >>
> >>  class SubClass(BaseClass):
> >>   def __init__(self, t, *args, **kw):
> >>     BaseClass.__init__(self, *args, **kw)
> >>     # do something with t
> >>
> >>  This does mean that the special sub class argument has to come before
> >>  the base class arguments when you create instances.
> >>
> >>  Whether you call BaseClass.__init__ early or late in the subclass init
> >>  method could depend on what your classes are doing.  Remember, in
> >>  Python, __init__ only initializes objects, it doesn't create them.
> >>  It's just another bit of code that you can call whenever you want.
> >>
> >>  --
> >>  John.
> >>
> >>
> >> _______________________________________________
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> >>
> > _______________________________________________
> > Tutor maillist  -  Tutor at python.org
> > http://mail.python.org/mailman/listinfo/tutor
> > 
> 
> 
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
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