Python Temperature class converter (K,F,C)

Question

Here's what's I'm trying to do : I want to code a working python class that convert everything by himself just by giving it a random value.

What I want exactly is the following :

>>> first=Temperature()
>>> first.celsius = 60
>>> first.kelvin
333.15
>>> first.fahrenheit
140

And whatever the first descriptor I set-up, I want the others to convert by themselves, even if I do the following :

>>> first.celsius = 60
>>> first.kelvin
333.15
>>> first.celsius += 1
>>> first.kelvin
334.15

Here's the code I've been working on :

class Celsius:
    def __get__(self, instance, owner):
        return 5 * (instance.fahrenheit - 32) / 9
    def __set__(self, instance, value):
        instance.fahrenheit = 32 + 9 * value / 5
    def __set__(self, instance, value):
        instance.kelvin = value + 273.15

class Temperature:
    celsius = Celsius()
    def __init__(self):
        self.fahrenheit = 0
    def __init__(self):
        self.kelvin = 0

Some things are working, but the convert back is not working well and it makes some errors but I really don't know how to make this work, would appreciate some help, even if you guys give me a 20 pages documentation.

Answer 1

What you need are properties. Use one common internal value and set it based on the property set:

class Temperature:
    def __init__(self):
        self.__kelvin = 273.15

    @property
    def kelvin(self):
        return self.__kelvin

    @property
    def celsius(self):
        return self.__kelvin - 273.15

    @property
    def fahrenheit(self):
        return (self.__kelvin - 273.15) * 9 / 5 + 32

    @kelvin.setter
    def kelvin(self,value):
        self.__kelvin = value

    @celsius.setter
    def celsius(self,value):
        self.__kelvin = value + 273.15

    @fahrenheit.setter
    def fahrenheit(self,value):
        self.__kelvin = (value - 32) * 5 / 9 + 273.15

    def __repr__(self):
        return f'Temperature(__kelvin={self.__kelvin})'

    def __str__(self):
        return f'{self.kelvin:.2f}\N{DEGREE SIGN}K/{self.celsius:.2f}\N{DEGREE SIGN}C/{self.fahrenheit:.2f}\N{DEGREE SIGN}F'

first = Temperature()
print(first)
first.kelvin = 0
print(first)
first.fahrenheit = 212
print(first)
first.celsius = 10
print(first)

Output:

273.15°K/0.00°C/32.00°F
0.00°K/-273.15°C/-459.67°F
373.15°K/100.00°C/212.00°F
283.15°K/10.00°C/50.00°F