Chapter 13 – Class and Type

Overview

This chapter explores Python’s approach to type and how it relates to classes and instances. It clarifies what “type” means in Python and how strong vs. dynamic typing is realized. :contentReference[oaicite:3]{index=3}

Three Types of Type

There are multiple notions of type in programming:

• The runtime type of an object (type(obj))

• The static annotated type (type hints)

• Conceptual type based on behavior

Primitive Data Types

Built‑in types like int, str, and float have fixed behaviors but are still Python objects.

Class‑Based Type

Every class defines a type. When you create a class, you create a new type.

Hierarchical Typing

Python’s inheritance hierarchy means types can participate in subclass relationships. For example:

isinstance(obj, Base)

Instance and Subclass

isinstance and issubclass help test whether an object belongs to a type or whether a class is derived from another.

Duck Typing

Python generally uses duck typing — if an object has the right methods and attributes, its type often doesn’t matter for correctness:

def quack(duck):
    duck.quack()

As long as duck has a quack method, this works irrespective of actual type.

Summary

Python’s notion of type combines runtime objects, class definitions, and behavioral expectations rather than rigid compile‑time constraints.