Example of the usage of built-in property() function.

property.py

class Circle(object):
    def __init__(self, radius):
        self._radius = radius

    def _get_radius(self):
        return self._radius
    def _set_radius(self, value):
        self._radius = value
    def _del_radius(self):
        del self._radius
    radius = property(_get_radius, _set_radius, _del_radius, "The radius of the Circle.")