A question about inheritance

[arserlom]

Hello I have a question about inheritance in Python. I'd like to do
something like this:

 class cl1:
  def __init__(self):
   self.a = 1

 class cl2(cl1):
  def __init__(self):
   self.b = 2

But in such a way that cl2 instances have atributes 'b' AND 'a'.
Obviously, this is not the way of doing it, because the __init__
definition in cl2 overrides cl1's __init__.

Is there a 'pythonic' way of achieving this?

Armando Serrano

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Re: A question about inheritance

[arserlom]

Thanks.

Jp Calderone wrote:
> On 8 May 2005 12:07:58 -0700, [EMAIL PROTECTED] wrote:
> >Hello I have a question about inheritance in Python. I'd like to do
> >something like this:
> >
> > class cl1:
> >  def __init__(self):
> >   self.a = 1
> >
> > class cl2(cl1):
> >  def __init__(self):
> >   self.b = 2
> >
> >But in such a way that cl2 instances have atributes 'b' AND 'a'.
> >Obviously, this is not the way of doing it, because the __init__
> >definition in cl2 overrides cl1's __init__.
> >
> >Is there a 'pythonic' way of achieving this?
>
> class cl2(cl1):
> def __init__(self):
> cl1.__init__(self)
> self.b = 2
> 
>   Jp

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Modifying CallTips.py to work with with new-style classes in IDLE.

[arserlom]

When using Idle, Call Tips are floating windows which display function,
class, and method parameter and docstring information when you type an
opening parenthesis, and which disappear when you type a closing
parenthesis.

But when you use new-style classes, they don't work fine and don't show
the arguments of the __init__ method.

There is a topic in this newsgroup (new style classes and an IDLE
"grump"), where a solution was given to the problem (in Mar 27 2002):

> The solution seems to be simply changing line 115 in CallTips.py (in
the
> Tools/Idle/ directory) as folows:
>
> if type(ob)==types.ClassType:
>
>   to
>
> if type(ob)==types.ClassType or type(ob) == types.TypeType:

I've tried it (Python 2.4.1 - IDLE 1.1.1) and it works fine (CallTips
was in the \Lib\idlelib directory for me).

Why isn't this the default behaviour? Is this the right place to post
this?

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Re: A question about inheritance

[arserlom]

Ok, thanks. I didn't know about new-style classes (I had learned python
from a book prior to them).

After reading about new-style classes, I find that your solution is
better because, using super (in general) avoids cl2 from having to know
the implementation details of cl1. This is  clearly explained in:

http://www.python.org/2.2.3/descrintro.html#cooperation

Also, when using new-style classes with IDLE, I found some problems
which I talk about in "Modifying CallTips.py to work with with
new-style classes in IDLE.", which I posted in this group.

Steven Bethard wrote:
> [EMAIL PROTECTED] wrote:
> > Hello I have a question about inheritance in Python. I'd like to do
> > something like this:
> >
> >  class cl1:
> >   def __init__(self):
> >self.a = 1
> >
> >  class cl2(cl1):
> >   def __init__(self):
> >self.b = 2
> >
> > But in such a way that cl2 instances have atributes 'b' AND 'a'.
> > Obviously, this is not the way of doing it, because the __init__
> > definition in cl2 overrides cl1's __init__.
> >
> > Is there a 'pythonic' way of achieving this?
>
> If there's a chance you might have multiple inheritance at some point
in
> this hierarchy, you might also try using super:
>
> class cl1(object): # note it's a new-style class
>  def __init__(self):
>  self.a = 1
>
> class cl2(cl1):
>  def __init__(self):
>  super(cl2, self).__init__()
>  self.b = 2
>
> Note that you probably want a new-style class even if you chose not
to
> use super in favor of Jp Calderone's suggestion.  There are very few
> cases for using old-style classes these days.
> 
> STeVe

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