Simple Python classproperty decorator

This module provides a simple way for defining class properties.

Deprecation notice: Starting with Python 3.9 the @classmethod descriptor can now wrap other descriptors like @property. See the official documentation for the announcement: https://docs.python.org/3.9/library/functions.html#classmethod

This means if you are using Python >= 3.9 you can simply realize a classproperty with:

class NewClass():
    _atr = "val"

    @classmethod
    @property
    def attr(cls):
        return cls._atr

So in this case this package is not needed anymore. I will still try to maintain this package until Python 3.8 reaches EOL which will be in October 2024.

Install

You can install this Python module via pip:

pip install simple-classproperty

Otherwise the module can be downloaded from PyPI: https://pypi.org/project/simple-classproperty/

Usage

1. Import the module:

   from simple_classproperty import ClasspropertyMeta, classproperty
   

2. Create a class with a class property:

   class NewClass(metaclass=ClasspropertyMeta):
       _attr = "val"
   
       @classproperty
       def attr(cls):
           return cls._attr
   

   Don't forget to set the metaclass!
3. (Optional) Define also a setter and deleter for the newly created class property (this works like the standard python property):

   @attr.setter
   def attr(cls, value):
       cls._attr = value
   
   @attr.deleter
   def attr(cls):
       del cls._attr
   

Tips

The classproperty is also accessible from an instance:

instance = NewClass()
print(instance.attr)  # "val"

When the value of the property is changed from an instance object, the class property will be changed. All other instances will have this new value:

instance1 = NewClass()
instance2 = NewClass()

instance1.attr = "new"

print(instance1.attr)  # "new"
print(instance2.attr)  # "new"
print(NewClass.attr)   # "new"

This behavior is the same when a property gets deleted from an instance.