Understanding __get__ and __set__ and Python descriptors

Question

I am trying to understand what Python\'s descriptors are and what they are useful for. I understand how they work, but here are my doubts. Consider the following co

Answer 1

I tried (with minor changes as suggested) the code from Andrew Cooke's answer. (I am running python 2.7).

The code:

#!/usr/bin/env python
class Celsius:
    def __get__(self, instance, owner): return 9 * (instance.fahrenheit + 32) / 5.0
    def __set__(self, instance, value): instance.fahrenheit = 32 + 5 * value / 9.0

class Temperature:
    def __init__(self, initial_f): self.fahrenheit = initial_f
    celsius = Celsius()

if __name__ == "__main__":

    t = Temperature(212)
    print(t.celsius)
    t.celsius = 0
    print(t.fahrenheit)

The result:

C:\Users\gkuhn\Desktop>python test2.py
<__main__.Celsius instance at 0x02E95A80>
212

With Python prior to 3, make sure you subclass from object which will make the descriptor work correctly as the get magic does not work for old style classes.