SOLID Principles Explained: How Single Responsibility Improves Python Code

The Single Responsibility Principle (SRP), the 'S' in SOLID, states that a class should have only one reason to change. A common violation occurs when a single class handles validation, database persistence, and email notifications together, making changes risky and testing complex. When unrelated concerns share the same class or method, a change to one — such as an email template update — can inadvertently break another, like user validation logic. Applying SRP means splitting such a bloated class into focused, independent components, each responsible for exactly one concern. This approach leads to isolated changes, easier unit testing, and code that is simpler for new developers to understand and maintain.