design-patterns

Python adaptation of the Head First Design Patterns (HFDP) book by Freeman, Robson, Bates and Sierra.

What is a (design) pattern?

A solution to a problem in context. In detail [HFDP]:

• The context is the situation in which the pattern applies, which should be a recurring situation;
• The problem refers to the objective, together with any constraints;
• The solution is the end goal: a general design that anyone can apply;

Summary of the design principles

The parentheses identify the chapter on which the principle was first applied, i.e (1) = chapter 1.

1. (1) Identify the aspects of your application that vary and separate them from what stays the same - i.e, encapsulate what varies;
2. (1) Program to an interface, not an implementation;
3. (1) Favor composition over inheritance;
4. (2) Strive for loosely coupled designs between objects which can interact;
5. (3) Open-closed principle: Classes should be open for extension but closed for modification;
6. (4) Dependency inversion principle: Depend on abstractions, do not depend on concrete classes. See chapter_4 for more details;
7. (7) Principle of least knowledge: Talk only to your immediate friends. See chapter_7 for more details;
8. (8) The Hollywood principle: Do not call us, we call you! See chapter_8 for more details;
9. (9) The principle of single responsibility: A class should only have one reason to change;

For more details, see the Markdown files in Chapters 4, 7 and 8.