https://en.wikipedia.org/wiki/Observer_pattern
- https://docs.python.org/2/reference/datamodel.html#object.__setattr__ - https://github.com/ipython/traitlets/#callbacks-when-a-trait-attribute-change - https://traitlets.readthedocs.io/en/stable/using_traitlets.html#observe @observe decorator https://en.wikipedia.org/wiki/Reactive_programming On Wednesday, October 19, 2016, kirby urner <kirby.ur...@gmail.com> wrote: > > Speaking of sharing Python with math teachers, not just > librarians (the bravest I sometimes thing), I included this > Circle in the session last night (adults learning, andragogy > at work): > > 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 = self.area / (2 * 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) > the_circle = Circle(5)print("the_circle:", the_circle)print("Area: ", > the_circle.area)the_circle.area = 50print("Radius when Area=50:", > the_circle.radius) > > That's right, the area changes if you set the radius > attribute and the other way around. I'm not claiming > to be the first to think of doing this. > > We're free to program a lot of geometric types like > that, that keep track of their own area and volume (a > theme at thekirbster.pythonanywhere.com as well, > the tiny Flask application I use as a classroom demo). > > Here's the Jupyter Notebook I put together before > class, where the above Circle type appears: > > https://github.com/4dsolutions/Python5/blob/master/Descriptors%20and% > 20Properties.ipynb > > (also viewable in nbviewer.jupyter.org, just paste > in the URL). > > Kirby > >
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