human
I am working on the file "Descriptors and Properties.ipynb".
The first task is:
Might we make both radius and area into properties, such that setting either recalculates the other?  
Let's try:
Can you write Python program for it?
 ... What is a the Python program you requested?
assistant
#Here is the Python program you requested.

import unittest

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)
        
    @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)
    
class TestCircle(unittest.TestCase):

    def testArea(self):
        the_circle = Circle(1)
        self.assertEqual(the_circle.area, math.pi, "Uh oh")
        
    def testRadius(self):
        the_circle = Circle(1)
        the_circle.area = math.pi * 4 # power rule
        self.assertEqual(the_circle.radius, 2, "Uh oh")

a = TestCircle()  # the test suite
suite = unittest.TestLoader().loadTestsFromModule(a) 
unittest.TextTestRunner().run(suite)  # run the test suite