property and virtuality

[Laszlo Zsolt Nagy]

My problem is about properties and the virtuality of the methods. I 
would like to create a property whose get and set methods
are virtual. I had the same problems in Delphi before and the solution 
was the same. I created a private _get method and a public
get method. The former one will call the latter. The same stands for 
_set and set. Here is an example below:

class C1(object):
    def namechanged(self):
        """Called after the name of the component has been changed."""
        pass
    def getname(self):
        """Returns the name of the component.
       
        You can override this method to provide generated component 
names."""
        return self._name
    def setname(self,name):
        """Set the name of the component.
       
        You can override this method to programatically control 
component name changes.
        """
        self._name = name
        self.namechanged()
    def _getname(self):
        """Internal method, do not use"""
        return self.getname()
    def _setname(self,name):
        """Internal method, do not use"""
        self.setname(name)
    name = property(_getname,_setname,"Name")

class C2(C1):
    def getname(self):
        return "lala"

class C3(C1):
    def _getname(self):
        return "lala"
    name = property(_getname,None,"Name")


c1 = C1()
c2 = C2()
c3 = C3()

c1.name = 'Test1'
c2.name = 'Test2'
c3.name = 'Test3'
print c1.name # This will print 'Test1'
print c2.name # This will print 'lala'
print c3.name # This will print 'lala'
print C3.name is C1.name # False

I cannot override C2._getname instead, because c2.name would print 
'Test2" instead of lala. Clearly, the property stores a reference to the 
get and set methods and it is not possible to have it use the new 
methods.  Creating a new property is the worst - need to duplicate code 
and also C3.name is C1.name returns False. :-) It is not a big problem 
because I found the solution just I wonder if there is a better way to 
"virtualize" property get/set functions.

 


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  Laszlo Nagy		      web: http://designasign.biz
  IT Consultant		      mail: gandalf at geochemsource.com

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