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.

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 allows to be 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):  # Some getter
        return cls._some_variable

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

ClassPropertiesMixin allows you to use a setter for properties, 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 some standard pattern, mainly:

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

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

import classutilities

class SomeConfigClass(classutilities.ConfigClassMixin):
    # This is OK:
    DATABASE_HOST = "localhost"
    DATABASE_NAME = "testing"
    # ...
    # This is NOT ok:
    database_password = "pass"  # NO! Must be lowercase
    # This is OK:
    @classmethod
    def connect_to_database(cls):
        return ...
    # This is NOT OK:
    def check_parameters(self):  # No instance-level methods
        ...

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