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

[arserlom]

Thanks.

Jp Calderone wrote:

On 8 May 2005 12:07:58 -0700, ar******@gmail. com 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__(se lf)
self.b = 2

Jp

[Steven Bethard]

ar******@gmail. com 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

[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:

ar******@gmail. com 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