Chapter 5. Cython and Extension Types

Make everything as simple as possible, but not simpler.

A. Einstein

In Chapter 3, we covered the fundamentals of what Cython adds to the Python language, and the power and control those additions provide. That chapter focused on basic data types and functions. Cython can enhance Python classes as well. Before we learn the specifics, we must first review the difference between Python classes and extension types, which will help us understand the what and why of Cython’s approach.

Comparing Python Classes and Extension Types

In Python everything is an object. What does that mean, specifically? At its most basic level, an object has three things: identity, value, and type. An object’s identity distinguishes it from all others and is provided by the id built-in function. An object’s value is simply the data associated with it, accessible via dot notation. Typically Python places an object’s data inside an internal instance dictionary named __dict__. The third essential attribute of any object is its type, which specifies the behaviors that an object of that type exhibits. These behaviors are accessible via special functions, called methods. A type is responsible for creating and destroying its objects, initializing them, and updating their values when methods are called on the object. Python allows us to create new types, in Python code, with the class statement.

We will see in this chapter how Cython allows low-level C access to an object’s data ...

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