By: Chris Harvey

Python Classes

NamespacesA mapping from names to objectsDifferent namespaces have different

mappingsNamespaces have varying lifetimes

Name Object

a 5

b 8

c 13

Name Object

x 8

fibonacci

function

result 21

Name Object

abs function

range function

True 1

ScopesRegion of code with access to a specific

namespaceAt any point, several scopes can be accessedThe most local scope is accessed first

Name Object

a 5

b 8

c 13

Name Object

x 8

fibonacci

function

result 21

Name Object

abs function

range function

True 1

Class Definition SyntaxDefinition formed

by a block of statements

A new namespace is created during class definition

A class must be defined before usage

Class ObjectsClass definition

itself has attributes

Class definition can be instantiated

Initialization methods can be added to class definitions

Instance Objects

All attributes of class object exist on instance

Instance can have attributes that are different from the class definition

Method Objects

Methods can be referred to by a name and called later

When a method is called the object it is called on is passed as first argument

By convention, the calling object argument is named self

InheritanceA class can inherit the

attribute of another class or classes

A name is matched to the first base class found with depth-first, then left-to-right

Types can be checked using isinstance(object,type) and issubclass(type,baseType)

Private VariablesNo such thing as truly

private variables

By convention, an underscore denotes a private member

Two underscores prefixed and up to one suffixed indicates name mangling

IteratorsClasses that represent

collections can offer iterators

Special __iter__ and __next__ methods must be created for traversing collection

Next() raises a StopIteration exception when no more elements exist

GeneratorsCreation of iterators

can be simplified

Use keyword yield to designate elements of collection

All iterator functionality created automatically