Defining class attributes + inheritance

[Santoso Wijaya]

Remember the mantra, "Explitic is better than implicit." ;-)

~/santa


On Tue, Mar 8, 2011 at 7:15 PM, Martin De Kauwe <mdekauwe at gmail.com> wrote:

> On Mar 9, 12:53 pm, "Rhodri James" <rho... at wildebst.demon.co.uk>
> wrote:
> > On Wed, 09 Mar 2011 01:00:29 -0000, Martin De Kauwe <mdeka... at gmail.com>
>
> > wrote:
> >
> > > class BaseClass(object):
> > >    def __init__(self, a, b, c, d):
> > >         self.a = a
> > >         self.b = b
> > >         self.c = c
> > >         self.d = d
> >
> > > class NewClass(BaseClass):
> > >     def __init__(self):
> > >         super(NewClass, self).__init__(new)
> > >         self.new = new
> > >         print self.new
> >
> > Two things leap out immediately.  First, BaseClass.__init__ takes four
> > parameters besides `self`, but when you call it you only give it one
> > parameter, `new`.  It's not going to like that.  Second, where did `new`
>
> > come from?  It's not a parameter to NewClass.__init__, and it doesn't
> seem
> > to be a global.  That's not going to work well either.
> >
> > However neither of these things are what the traceback is complaining
> > about.
> >
> > >  if __name__ == "__main__":
> >
> > >     A = PreviousClass(1, 2, 3, 4, 5)
> > >     B = NewClass(1, 2, 3, 4, 5)
> >
> > > $ python test.py
> > > Traceback (most recent call last):
> > >   File "model_data.py", line 29, in <module>
> > >     B = NewClass(1, 2, 3, 4, 5)
> > > TypeError: __init__() takes exactly 1 argument (6 given)
> >
> > When you create your NewClass, you give it five parameters (1, 2, 3, 4,
> 5)
> > plus the implicit `self`, which is the "(6 given)" part of the message.
> > However NewClass.__init__ takes no parameters aside from `self` (i.e. it
>
> > "takes exactly 1 argument").  There's a mismatch between what you've told
>
> > NewClass.__init__ to expect and what you actually deliver to it.
> >
> > The point that may be confusing you is that NewClass.__init__ knows
> > nothing at all about BaseClass.__init__.  It doesn't inherit parameters
> >  from it or anything magical like that; you have to tell it everything.
>  If
> > you want parameters to pass from NewClass.__init__ to BaseClass.__init__
>
> > you will have to provide them somehow.  In this case, I think what you
> > meant was something like this:
> >
> > class NewClass(BaseClass):
> >      def __init__(self, a, b, c, d, new):
> >          super(NewClass, self).__init__(a, b, c, d)
> >         self.new = new
> >          # etc
> >
> > --
> > Rhodri James *-* Wildebeest Herder to the Masses
>
> Yep that was it, I think I misunderstood and assumed it knew about
> stuff in the BaseClass constructor. All makes sense now!
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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