How Can I Use Property Decorators with Class Methods in Python?

Using Property Decorators with Class Methods (classmethod)

The property() decorator in Python allows one to define a property on a class, which provides access to a specific attribute. However, when using the property() decorator with methods marked as class methods using @classmethod, an issue arises as classmethods are not callable on instances.

Solution for Python 2 and Python 3 (including 3.9-3.10)

Since properties in Python operate on instances rather than classes, a workaround can be implemented using metaclasses. In Python metaclasses are responsible for creating classes dynamically and can be utilized to add properties to the class itself. Here's a slightly modified code snippet:

class foo(object):
    _var = 5
    class __metaclass__(type):  # Metaclass definition (Python 2 syntax)
        @property
        def var(cls):
            return cls._var
        @var.setter
        def var(cls, value):
            cls._var = value

# Access and modify the class-level property using the class name
foo.var  # Get the initial value
foo.var = 3  # Set the value

By defining the property within the metaclass, it affects the class itself, enabling it to possess a class-level property accessible via the class name.

Alternative Method for Python 3.8 and Above

In Python versions 3.8 and above, the @classmethod decorator can be used in conjunction with the property() decorator. The following code snippet demonstrates:

class Foo(object):
    _var = 5

    @classmethod
    @property
    def var(cls):
        return cls._var

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

# Access and modify the class-level property using the class name
Foo.var  # Get the initial value
Foo.var = 3  # Set the value

In this case, both the @classmethod and @property decorators can be applied to the same method, allowing for the definition of a class-level property using class methods.

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