Clean Code in Python

References

Here is a list of information you can refer to:

• GoF: The book written by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides named Design Patterns: Elements of Reusable Object-Oriented Software
• SNGMONO: An article written by Robert C. Martin, 2002 named SINGLETON and MONOSTATE
• The Null Object Pattern, written by Bobby Woolf