The simplest form of class definition looks like this:
class ClassName:
<statement-1>
.
.
.
<statement-N>
Class definitions, like function definitions (def statements) must be executed before they have any effect. (You could conceivably place a class definition in a branch of an if statement, or inside a function.)
In practice, the statements inside a class definition will usually be function definitions, but other statements are allowed, and sometimes useful - we'll come back to this later. The function definitions inside a class normally have a peculiar form of argument list, dictated by the calling conventions for methods - again, this is explained later.
When a class definition is entered, a new name space is created, and used as the local scope - thus, all assignments to local variables go into this new name space. In particular, function definitions bind the name of the new function here.
When a class definition is left normally (via the end), a class object is created. This is basically a wrapper around the contents of the name space created by the class definition; we'll learn more about class objects in the next section. The original local scope (the one in effect just before the class definitions was entered) is reinstated, and the class object is bound here to class name given in the class definition header (ClassName in the example).