[Edu-sig] a Circle type with radius, area both properties (fixed)

[Wes Turner]

On Thu, Oct 20, 2016 at 9:45 PM, kirby urner <kirby.urner at gmail.com> wrote:

>     @area.setter
>>     def area(self, value):
>>         self._area = value
>>         self._radius = self.area / (2 * math.pi)
>>
>>
> Uh oh...  I'm in the middle of teaching Session 10
> and couldn't figure out why my radius for a smaller
> area was bigger.  Couldn't be.  I did my algebra
> wrong, duh.
>


https://docs.python.org/2/library/unittest.html

if __name__ == "__main__":
    # import unittest
    unittest.main()



> Here's the debugged version:
>
> # -*- coding: utf-8 -*-
> """
> Created on Thu Oct 20 15:43:14 2016
>
> @author: Kirby Urner
>
> toggle the import model_property on and off to see
> the example works the same either way.  model_property
> contains a pure Python emulator of the built in
> property type.
>
> Related reading:
> https://mail.python.org/pipermail/edu-sig/2016-October/011548.html
> """
>
> from model_property import Property as property
> import math
>
> class Circle:
>     """setting either the radius or area attribute sets the other
>        as a dependent value.  Initialized with radius only, unit
>        circle by default.
>     """
>
>     def __init__(self, radius = 1):
>         self.radius = radius
>
>     @property
>     def area(self):
>         return self._area
>
>     @property
>     def radius(self):
>         return self._radius
>
>     @area.setter
>     def area(self, value):
>         self._area = value
>         self._radius = math.sqrt(self._area / math.pi)  #duh
>
>     @radius.setter
>     def radius(self, value):
>         self._radius = value
>         self._area = math.pi * (self._radius ** 2)
>
>     def __repr__(self):
>         return "Circle(radius = {})".format(self.radius)
>
> the_circle = Circle(5)
> print("the_circle:", the_circle)
> print("Area: ", the_circle.area)
> the_circle.area = 50
> print("Radius when Area=50:", the_circle.radius)
>
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