How to call a data member of the base class if it is being overwritten as a property in the derived class?

Question!

This question is similar to this other one, with the difference that the data member in the base class is not wrapped by the descriptor protocol.

In other words, how can I access a member of the base class if I am overriding its name with a property in the derived class?

class Base(object):
    def __init__(self):
    	self.foo = 5

class Derived(Base):
    def __init__(self):
    	Base.__init__(self)

    @property
    def foo(self):
    	return 1 + self.foo # doesn't work of course!

    @foo.setter
    def foo(self, f):
    	self._foo = f

bar = Base()
print bar.foo

foobar = Derived()
print foobar.foo

Please note that I also need to define a setter because otherwise the assignment of self.foo in the base class doesn't work.

All in all the descriptor protocol doesn't seem to interact well with inheritance...

By : UncleZeiv


Answers

once you have property with same name 'foo' it overrides the behaviour of access of name 'foo' only way out seems that you explicitly set 'foo' in dict

btw: I use python 2.5 hence had to change code a bit

class Base(object):
    def __init__(self):
        self.foo = 5

class Derived(Base):
    def __init__(self):
        Base.__init__(self)

    def g_foo(self):
        return 1   self.__dict__['foo'] # works now!

    def s_foo(self, f):
        self.__dict__['foo'] = f
        self._foo = f

    foo = property(g_foo, s_foo)

bar = Base()
print bar.foo

foobar = Derived()
print foobar.foo


Honestly, the thing to look at here is that you're trying to twist your code around a design that is simply poor. The property descriptors handle the request for a 'foo' attribute, and you want to bypass these completely, which is just wrong. You're already causing Base.init to assign foobar._foo = 5, so thats exactly where the getter needs to look, too.

class Base(object): def init(self): self.foo = 5

class Derived(Base):
  def __init__(self):
    Base.__init__(self)

  @property
  def foo(self):
    return 1   self._foo # DOES work of course!

  @foo.setter
  def foo(self, f):
    self._foo = f

bar = Base()
print bar.foo

foobar = Derived()
print foobar.foo


class Foo(object):
    def __new__(cls, *args, **kw):
        return object.__new__(cls, *args, **kw)

    def __init__(self):
        self.foo = 5

class Bar(Foo):
    def __new__(cls, *args, **kw):
        self = object.__new__(cls, *args, **kw)
        self.__foo = Foo.__new__(Foo)
        return self

    def __init__(self):
        Foo.__init__(self)

    @property
    def foo(self):
        return 1   self.__foo.foo

    @foo.setter
    def foo(self, foo):
        self.__foo.foo = foo

bar = Bar()
bar.foo = 10
print bar.foo
By : mtasic85


This video can help you solving your question :)
By: admin