python - Override a field in parent class with property in child class -

where looks this:

class a(object):     def __init__(self, val):         self.x=val         self.y=42         # other fields  class b(object):     def __init__(self):         self.a=22         # other fields  class c(a,b):     def __init__(self, val):         super(c,self).__init__(val)     @property     def x(self):         # if a.x none return value can compute a.y , b.a         # if a.x not none return     @x.setter     def x(self, val):         # set field value 

sometimes want set assumed value x hand, in case use a. in other cases want use more complicated approach involves computing a.x's value on basis of information organized b. idea in code make c class can a (in terms of x field) doesn't need field value set hand, instead gets derived.

what can't figure out how have c.x property shadow a.x field in sensible way.

the line self.x = val in a.__init__ method invoke c.x setter. have handled here. handling per instance attributes here, not attributes on class inherited subclasses.

all need set different attribute in setter represent x value. name _x, example:

class c(a, b):     _x = none      @property     def x(self):         if self._x not none:             return self._x         return self.a + self.y      @x.setter     def x(self, val):         self._x = val 

note if c.__init__ call super().__init__, don't need @ all. however, do need make sure @ least a.__init__() plays along in inheritance structure; add in more calls super().__init__():

class a(object):     def __init__(self, val, *args, **kwargs):         super(a, self).__init__(*args, **kwargs)         self.x = val         self.y = 42  class b(object):     def __init__(self, *args, **kwargs):         super(b, self).__init__(*args, **kwargs)         self.a = 22 

using *args , **kwargs allows these methods pass on arguments other classes in hierarchy.

demo, using above classes:

>>> c = c(none) >>> c.x 64 >>> c.x = 15 >>> c.x 15