Re: Class Variable Inheritance

[Scott David Daniels]

Brian Jones wrote:
class a(object):
    mastervar = []
    def __init__(self):
        print 'called a'
class b(a):
    def __init__(self):
        print 'called b'
        self.mapvar()
    def mapvar(self):
        self.mastervar.append(['b'])
class c(b):
      mastervar = []   # Adding this should make things clearer
    def __init__(self):
        print 'called c'
        self.mapvar()
    def mapvar(self):
        super(c, self).mapvar()
        self.mastervar.append(['c'])
if __name__ == '__main__':
    a1 = a()
    b1 = b()
    c1 = c()
    d1 = c() # Call C again
      for object in a1, b1, c1, d1:
          print id(object.mastervar), object.mastervar
What I don't understand is why mastervar gets modified by each _seperate 
instance_ of classes that happen to extend the base class 'a'. Shouldn't 
mastervar be contained within the scope of the inheriting classes?  Why 
is it being treated like a global variable and being modified by the 
other instances?
By over-riding mastervar in class c, I hope I've shown that a class 
variable is shared by all of its instances, but can be over-ridden by
a subclass's class variable.

--Scott David Daniels
[EMAIL PROTECTED]
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