How to Define Class Properties in Python

In Python, you can add methods to a class using the @classmethod decorator. But is there a similar mechanism for defining class properties?

Certainly. Python provides the @classproperty decorator for this purpose. Its syntax and usage closely resemble that of @classmethod:

class Example(object):
    the_I = 10
    
    @classproperty
    def I(cls):
        return cls.the_I

The @classproperty decorator creates a class property named I. You can access this property directly on the class itself, like so:

Example.I  # Returns 10

If you want to define a setter for your class property, you can use the @classproperty.setter decorator:

@I.setter
def I(cls, value):
    cls.the_I = value

Now you can set the class property directly:

Example.I = 20  # Sets Example.the_I to 20

Alternative Approach: ClassPropertyDescriptor

If you prefer a more flexible approach, consider using the ClassPropertyDescriptor class. Here's how it works:

class ClassPropertyDescriptor(object):

    def __init__(self, fget, fset=None):
        self.fget = fget
        self.fset = fset

    # ... (method definitions)

def classproperty(func):
    return ClassPropertyDescriptor(func)

With this approach, you can define class properties as follows:

class Bar(object):

    _bar = 1

    @classproperty
    def bar(cls):
        return cls._bar

You can set the class property using its setter (if defined) or by modifying its underlying attribute:

Bar.bar = 50
Bar._bar = 100

This expanded solution provides more control and flexibility when working with class properties in Python.