A class definition defines a class object (see section 3.2):
classdef: "class" classname [inheritance] ":" suite inheritance: "(" [expression_list] ")" classname: identifier
A class definition is an executable statement. It first evaluates the
inheritance list, if present. Each item in the inheritance list
should evaluate to a class object. The class's suite is then executed
in a new execution frame (see section 4.1), using a newly
created local namespace and the original global namespace.
(Usually, the suite contains only function definitions.) When the
class's suite finishes execution, its execution frame is discarded but
its local namespace is saved. A class object is then created using
the inheritance list for the base classes and the saved local
namespace for the attribute dictionary. The class name is bound to this
class object in the original local namespace.
Programmer's note: variables defined in the class definition are class variables; they are shared by all instances. To define instance variables, they must be given a value in the the __init__() method or in another method. Both class and instance variables are accessible through the notation ```codeself.name'', and an instance variable hides a class variable with the same name when accessed in this way. Class variables with immutable values can be used as defaults for instance variables.