Class utilities

Author: David Salac https://github.com/david-salac

Simple package with helpful utilities for classes. That includes class level properties and filters for configuration classes.

Note: this package does not require any external dependencies.

How to install package

Use PIP command:

pip install classutilities

How to use class level properties

Class level properties are properties defined on class level. They behave exactly the same as normal properties (but allow being called on class level and not only on instance level).

Consider the following example (defining class level properties):

import classutilities

class SomeClass(classutilities.ClassPropertiesMixin):
    _some_variable = 8  # Some class variable

    @classutilities.classproperty
    def some_variable(cls):  # Example of getter
        return cls._some_variable

    @some_variable.setter
    def some_variable(cls, value):  # Example of setter
        cls._some_variable = value

ClassPropertiesMixin allows you to use a setter for properties. However, if you only need a getter, it will work even without this mixin.

Usage of class-level properties:

# Getter:
value = SomeClass.some_variable
print(value)  # >>> 8

# Setter:
new_value = 9
SomeClass.some_variable = new_value
print(SomeClass.some_variable)  # >>> 9
print(SomeClass._some_variable)  # >>> 9

As you can see, class-level properties behave very naturally.

Configuration classes

Configuration classes usually follow standard patterns, mainly:

• All members have to be upper case (if they do not start with an underscore).
• There is no constructor in the class.
• There is no standard (instance) method in the class. Only class methods and static methods are allowed.

It is beneficial to have some validator for a configuration class that checks if all these conditions are followed. This is precisely what ConfigClassMixin does. Consider the following use-case:

import classutilities

class SomeConfigClass(classutilities.ConfigClassMixin):
    # This is OK:
    DATABASE_HOST = "localhost"  # OK: variable name in uppercase
    DATABASE_NAME = "testing"  # OK: variable name in uppercase
    # ...
    
    # This is NOT OK (class variables must be uppercase):
    database_password = "pass"  # NO: must not be lowercase
    
    # This is OK (underscore on the beginning):
    _api_version = "1.0.0"  # OK: starts with an underscore
    
    # This is OK:
    @classmethod
    def connect_to_database(cls):  # Class methods are acceptable
        return ...
    
    # This is OK:
    @staticmethod
    def check_status():  # Static methods are acceptable
        return ...
    
    # This is NOT OK:
    def check_parameters(self):  # No instance-level methods
        return ...

Mixin ConfigClassMixin can be used together with mixin for class-level properties. Class level properties are also acceptable (this filter allows them).