Python property returning property object

Question

I have a class like this:

class Foo(object):
    def __init__(self):
        self.bar = property(self.get_bar)

    def get_bar(self):
        return \"bar\"

pr         


        

Answer 1

The object is not instantiated.

class Foo(object):
  def get_bar(self):
    return "bar"

bar = Foo()
print(bar.get_bar)

Answer 2

You can also do it like shown here:

class Foo(object):
    def __init__(self):
        self._bar = None

    @property
    def bar(self):
        return self._bar

    @bar.setter
    def bar(self, value):
        self._bar = value

    @bar.deleter
    def bar(self):
        self._bar = None # for instance

which is equivalent to:

class Also_Foo(object):
    def __init__(self):
        self._bar = None

    def get_bar(self):
        return self._bar

    def set_bar(self, value):
        self._bar = value

    def del_bar(self):
        self._bar = None # for instance

    bar = property(fget=get_bar, fset=set_bar, fdel=del_bar, doc=None)

BUT without polluting the class namespace with get and set methods for each attribute.

You retain external direct access to the variable by using ._bar instead of .bar.

Answer 3

You need to make a minor change:

class Foo(object):

    def get_bar(self):
        return "bar"

    bar = property(get_bar)

print Foo().bar # prints bar

The property needs to be an attribute of the class, not the instance; that's how the descriptor protocol works.

Answer 4

You can do it like this

class Foo(object):
    def __init__(self):
        self.__bar = None

    def get_bar(self):
        return self.__bar

    def set_bar(self, value):
        self.__bar = value

    bar = property(get_bar, set_bar)

foo = Foo()
print foo.bar    # None
foo.bar = 1
print foo.bar    # 1