Unchangeable variables in a class?

[menator01]

Might could do something like this to keep from setting the value the way I did

@property
    def double(self):
        if self._double != self._value * 2:
            raise AttributeError
        return self._double

[Gribouillis]

Might could do something like this to keep from setting the value the way I did

A much better option is to not define a _double member

class MyNum(object):

    def __init__(self, value):
        self._value = value

    @property
    def value(self):
        return self._value

    @property
    def double(self):
        return self._value * 2

[deanhystad]

When an attribute depends on the value of another attribute, and the value of rither attribute can change, I think a method is better choice than using a variable.

Pick a subset of attributes that are needed to compute all attributes. These will become instance variables. Other attributes that are computed from the instance variables become methods. If you want them to look like instance variables you can make them properties.

class MyNum:
      
    def __init__(self, value):
        self.value = value

    @property
    def double(self):
        return self.value * 2

    @double.setter
    def double(self, value):
        self.value = value / 2