Programmer-defined types

We have used many of Python's built-in types; now we are going to define a new type. As an example, we will create a type called Point that represents a point in two-dimensional space. In mathematical notation, points are often written in parentheses with a comma separating the coordinates. For example, (0, 0) represents the origin, and (x, y) represents the point x units to the right and y units up from the origin.

There are several ways we might represent points in Python:

Creating a new type is more complicated than the other options, but it has advantages that will be apparent soon.

A programmer-defined type is also called a class. A class definition looks like this:

class Point:
    """Represents a point in 2-D space."""

The header indicates that the new class is called Point. The body is a docstring that explains what the class is for

Defining a class named Point creates a class object.

>>> Point
<class '__main__.Point'>

Because Point is defined at the top level, its "full name" is __main__.Point.

The class object is like a factory for creating objects. To create a Point, you call Point as if it were a function.

>>> blank = Point()
>>> blank
<__main__.Point object at 0xb7e9d3ac>

The return value is a reference to a Point object, which we assign to blank.

Creating a new object is called instantiation, and the object is an instance of the class.