How Can I Use the `property()` Decorator with Classmethods in Python?

Using property() on Classmethods

Python provides the property() decorator to create read-only or read-write attributes that are computed dynamically. However, when combined with classmethods, this approach faces some limitations.

In Python versions 3.8 and later, the property() decorator can be applied to classmethods directly, allowing for concise access to class attributes:

class Foo:
    _var = 5
    @classmethod
    @property
    def var(cls):
        return cls._var

    @classmethod
    @var.setter
    def var(cls, value):
        cls._var = value

However, in Python 2 and versions of Python 3 prior to 3.8, a different approach is required. Since properties are defined on instances, using them with classmethods involves creating the property on the class's metaclass:

class Foo(object):
    _var = 5

    class __metaclass__(type):
        def __init__(cls, name, bases, dict):
            super().__init__(name, bases, dict)
            cls.var = property(cls.getvar, cls.setvar)

        @classmethod
        def getvar(cls):
            return cls._var

        @classmethod
        def setvar(cls, value):
            cls._var = value

In this example, the __metaclass__ defines the property on the metaclass, which is then inherited by instances of the Foo class.

Alternatively, you can use the metaclass parameter to define a custom metaclass:

class FooMeta(type):
    def __init__(cls, name, bases, dict):
        super().__init__(name, bases, dict)
        cls._var = 5
        cls.var = property(cls.getvar, cls.setvar)

    @classmethod
    def getvar(cls):
        return cls._var

    @classmethod
    def setvar(cls, value):
        cls._var = value

class Foo(metaclass=FooMeta):
    pass

In this setup, the metaclass initializes the _var attribute and defines the var property. Instances of Foo will inherit the var property and be able to access the _var attribute accordingly.

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