Python: How To Copy All Attibutes From Base Class To Derived One

I want to achieve the following: #!/usr/bin/python class SuperHero(object): def setName(self, name): self.name = name def getName(self): return self.name

Solution 1:

Add a initiator function that copies across the __dict__ attribute:

classSuperMan(SuperHero): 
    def__init__(self, source=None):
        if source isnotNone:
            self.__dict__.update(source.__dict__)

The __dict__ of an instance holds all instance attributes, the above merely copies over all of those attributes to the new SuperMan instance.

Demo:

>>>classSuperHero(object): ...defsetName(self, name):...        self.name = name...defgetName(self):...return self.name...>>>classSuperMan(SuperHero): ...def__init__(self, source=None):...if source isnotNone:...            self.__dict__.update(source.__dict__)...>>>sh = SuperHero()>>>sh.setName("Clark Kent")>>>sm = SuperMan(sh)>>>print sm.getName() 
Clark Kent

Or, for a more terrible hack, you could swap out the class attribute:

sh = SuperHero()
sh.setName("Clark Kent")
sh.__class__ = SuperMan

but that can lead to more interesting bugs as you never called the SuperMan initializer and thus the expected state might be incorrect.

Solution 2:

I'd prefer explicit solution - copying one by one. Martijn Pieters's solution is nice, but with time your __dict__ may grow and you may not want to copy all it's content (or worse - forget about this fact and experience some nasty side effects). Besides the Zen of Python says: Explicit is better than implicit..

Side note - you are aware of properties, right? So your code could be more pythonic if you used them:

classSuperHero(object):@propertydefname(self):
        returnself._name
    @name.setter
    defname(self, name):
        self._name = name

sh = SuperHero()
sh.name = "Clark Kent"