CSC 203 Final: Class

create a class

Use the keyword class followed by a capitalized class name (each word is capitalized) and a : Then indent and define attributes and methods underneath.

class Dog:

»»»def __init__(self, breed, age):

»»»»»self.breed = breed

»»»»»self.age = age

»»»def method(self):

»»»»»return or print whatever

def __init__(self, parameters):

Initializer. Parameters go in parentheses; first is self, then optional parameters.

self

The first parameter in the __init__ method is a variable that refers to an instance

__init__ body

Where you initialize instance attributes, typically assigning parameters to self.attribute.

def __init__(self, age)

»»»self.age = age

Constructor

A method that creates and initializes an object (the __init__ method).

Creating an instance

instance_variable = ClassName(‘argument1’, argument2)

Python passes the self argument for you so only supply the needed parameters

Access attributes

Use dot notation

instance.attribute

Methods

functions that belong to a class. They define the behavior of objects created from the class. Always include self as first parameter.

Call a method

Use instance.method() if self is the only parameter

Class attributes

Shared data for all instances of a class. It’s not in any of the functions

Instance methods

uses self to access the instance attribute

Class

A blueprint for how objects look and behave.

self meaning

actual instance of the class that just makes sure that all the data sticks to the correct instance

Dot notation

Used to access methods or attributes:

instance.attribute

instance.method()

Encapsulation

make data private from client code.

Leading underscore convention

beginning an attribute with a single or double underscore means it’s private

_attribute

__attribute

def __add__(self, other):

same as + operator. It takes the current and other instance. Overloads + to define how two instances of a class should be added.

ClassName( ) is used inside the method because:

• You must return a brand new ClassName that represents the sum.

• You should not change the original instances.

operator overloading

Allows custom classes to define behavior for operators like +, *, [ ].

Calling __add__

Use instance1 + instance2.

def __iadd__(self, other):

same as +=. Modifies the self object so it equals the sum of self + other

Calling __iadd__

Use instance1 += instance2

def __repr__(self):

When defined in a class, the method returns a string representation of an instance

Calling __repr__

Use

• print(repr(instance))

• print(instance)