Fluent Python, 2nd Edition

Chapter 11. A Pythonic Object

For a library or framework to be Pythonic is to make it as easy and natural as possible for a Python programmer to pick up how to perform a task.

Martijn Faassen, creator of Python and JavaScript frameworks.¹

Thanks to the Python Data Model, your user-defined types can behave as naturally as the built-in types. And this can be accomplished without inheritance, in the spirit of duck typing: you just implement the methods needed for your objects to behave as expected.

In previous chapters, we studied the behavior of many built-in objects. We will now build user-defined classes that behave as real Python objects. Your application classes probably don’t need and should not implement as many special methods as the examples in this chapter. But if you are writing a library or a framework, the programmers who will use your classes may expect them to behave like the classes that Python provides. Fulfilling that expectation is one way of being “Pythonic.”

This chapter starts where Chapter 1 ended, by showing how to implement several special methods that are commonly seen in Python objects of many different types.

In this chapter, we will see how to:

• Support the built-in functions that convert objects to other types (e.g., repr(), bytes(), complex(), etc.)

• Implement an alternative constructor as a class method

• Extend the format mini-language used by f-strings, the format() built-in, and the str.format() method

• Provide read-only access to attributes ...