At Thursday 21/9/2006 06:52, [EMAIL PROTECTED] wrote:
class animal:
def __init__(self, weight, colour):
self.weight = weight
self.colour = colour
class bird(animal):
def __init__(self, wingspan):
self.wingspan = wingspan
print self.weight, self.colour, self.wingspan
class fish(animal):
def __init__(self, length):
self.length = length
print self.weight, self.colour, self.length
So basically I have a base class (animal) that has certain attributes.
When animal is inherited by a specific instance, further attributes are
added, but I need to have access to the original attributes (weight,
colour). When I run my code from within the derived class, self.weight
and self.colour are not inherited (although methods are inherited as I
would have expected).
You have to call the base __init__ too. If a bird is some kind of
animal, it has a weight and a colour, and you have to provide them too:
class bird(animal):
def __init__(self, weight, colour, wingspan):
animal.__init__(self, weight, colour)
self.wingspan = wingspan
print self.weight, self.colour, self.wingspan
It seems from reading the newsgroups that a solution might be to
declare weight and colour as global variables in the class animal:
You can declare them as class attributes inside animal; this way they
act like a default value for instance attributes.
class animal:
weight = 0
colour = ''
...
I'm not very experienced with OOP techniques, so perhaps what I'm
trying to do is not sensible. Does Python differ with regard to
inheritance of member variables from C++ and Java?
They are not called "member variables" but "instance attributes".
They *are* inherited [1] but you have to set their value somewhere.
Any object can hold virtually any attribute - this is *not* usually
determined by the object's class.
Base constructors ("initializer" actually) are *not* invoked
automatically, so you must call them explicitely.
Read the Python Tutorial, it's easy and will teach you a lot of
things about the language. You can read it online at
<http://docs.python.org/tut/tut.html>
[1] kinda... remember that classes don't determine the available
attributes; class attributes are inherited, and any attribute you set
on an instance will be accessible by any method of the object, even
above in the hierarchy.
Gabriel Genellina
Softlab SRL
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