Using Python Descriptors to Enforce the Single Responsibility Principle

In everyday Python coding, using descriptors helps adhere to the Single Responsibility Principle (SRP) by separating attribute access logic from the main class, making code more Pythonic and maintainable.

A simple example shows a Car class with a fuel‑tank property validated via @property and @fuel_amount.setter, which quickly becomes cluttered as more attributes are added.

The article then introduces a descriptor class SixtyLitresCapacity that encapsulates the validation logic for a fuel amount between 0 and 60 liters, simplifying the Car class.

Key to a descriptor is implementing the __get__ and __set__ methods; these methods allow the descriptor to control attribute retrieval and assignment when assigned to a class attribute.

To make descriptors more flexible, a generic IsBetween descriptor is presented. It defines an

__init__(self, min_value, max_value, exception_type=ValueError)

to set bounds, and a __set_name__(self, owner, name) method so the descriptor knows the attribute name it manages.

With IsBetween, the same descriptor can validate various ranges, such as battery level, age, or temperature, and can raise custom exceptions for out‑of‑range values.

The article concludes that descriptors are a powerful tool for keeping classes focused on a single responsibility, improving code clarity and reusability.