MUDBytes Community - Viewing Topic: Classes & Inheritance

Confuto
Conjurer

Group: Members
Posts: 113
Joined: Nov 1, 2008

#1 Posted Nov 1, 2009, 6:31 pm

I think I found a solution to this a while ago, promptly forgot it and now can't remember where I found it. In any case, here's the issue:

Code (text):

>>> class A:
	def __init__(self):
		self.v1 = 1
		self.v2 = 2
 
 
>>> class B(A):
	def __init__(self):
		self.v2 = 4
		self.v3 = 3
 
 
>>> c = B()
>>> c.v3
3
>>> c.v2
4
>>> c.v1
 
Traceback (most recent call last):
  File "<pyshell#84>", line 1, in <module>
    c.v1
AttributeError: B instance has no attribute 'v1'
>>>

I can see why this is happening - B's init is overwriting A's completely. Is there a convenient way around this, so that I can leave v1 untouched in B while overwriting v2 and adding v3?

EDIT: Typo :(

Last edited Nov 1, 2009, 6:32 pm by Confuto

Idealiad
Sorcerer

Group: Members
Posts: 258
Joined: Jan 28, 2007

#2 Posted Nov 1, 2009, 6:43 pm

I think you want something like this:

Code (text):

 
class A(object):
    def __init__(self):
        self.v1 = 1
        self.v2 = 2
 
 
class B(A):
    def __init__(self):
        super(B, self).__init__()
        self.v2 = 4
        self.v3 = 3
 
c = B()
print c.v3, c.v2, c.v1
 
>C:\Python25\pythonw -u "testClass.py"
3 4 1
>Exit code: 0

Note that you need to explicitly declare A as a child of object for super() to work correctly.

Orrin
Sorcerer

Group: Moderators
Posts: 286
Joined: Aug 26, 2008

#3 Posted Nov 1, 2009, 6:59 pm

What about:

Code (text):

 
>>> class A(object):
...     def __init__(self):
...             self.v1 = 1
...             self.v2 = 2
...
>>> class B(A):
...     def __init__(self):
...             super(B, self).__init__()
...             self.v2 = 4
...             self.v3 = 3
...
>>> c = B()
>>> c.v3
3
>>> c.v2
4
>>> c.v1
1
>>>

Edit: Ninja'd!

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Last edited Nov 1, 2009, 7:01 pm by Orrin

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Confuto Conjurer Group: Members Posts: 113 Joined: Nov 1, 2008	#4 Posted Nov 1, 2009, 7:50 pm
	Perfect! Thank you both.