newb question about @property

Mon Oct 2 15:32:09 EDT 2017

Steve D'Aprano wrote:
> Circle didn't use any setters, but I could have let you set the 
> diameter, which in
> turn would set the radius:
>> circle.radius = 2
> assert circle.diameter == 4
> circle.diameter == 2 # requires a setter
> assert circle.radius == 1
>> Getting that to work is left as an exercise :-)
>It WAS a good exercise!! I was concerned about "infinite recursion" 
between my two property setters.. Thanks! Next? :)
Bill
import math
class Circle(object):
 """ Define a circle class with radius and diameter""" def __init__(self, radius):
 self.radius = radius
 self.diameter =2*radius
 @property def radius(self):
 return self._radius
 @radius.setter def radius(self, value):
 self._radius = value
 self._diameter=2*value
 @property def diameter(self):
 return self._diameter
 @diameter.setter def diameter(self, value):
 self._diameter = value
 self._radius = value /2 @property def area(self):
 return math.pi *self.radius **2 @property def circumference(self):
 return 2 * math.pi *self.radius
## Start here ## circle = Circle(1 / math.pi)
print("Area = {:.2f}".format(circle.area))
print("Circumference = {:.2f}".format(circle.circumference))
circle.radius =2 assert circle.diameter ==4 print("Area = {:.2f}".format(circle.area))
print("Circumference = {:.2f}".format(circle.circumference))
circle.diameter =2 # requires a setter assert circle.radius ==1 print("Area = {:.2f}".format(circle.area))
print("Circumference = {:.2f}".format(circle.circumference))