Defining class attributes + inheritance

[Martin De Kauwe]

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!