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Rubén Izquierdo Beviá, profile picture
Uploaded byRubén Izquierdo Beviá
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CLTL python course: Object Oriented Programming (1/3)

This document summarizes an introductory session on object-oriented programming in Python. It introduces key concepts of OOP like classes, objects, attributes, methods, encapsulation, inheritance and provides examples of defining classes for a Person and Bank Account. It also demonstrates how to define a class, create objects, access attributes and methods in Python. The benefits of OOP like code reusability, abstraction and inheritance are discussed.

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CLTL Python Course Object Oriented Programming in Python 1st session April 24th 2013
What is Object Oriented Programming ? ● Change of paradigm Procedural vs. Data oriented ● Procedural programming – Focus on functions or procedures – Usually process and data mixed in the code – Python basic datatypes (lists, dicts, tuples...) ● Data Oriented programming – Focus is the data – Process and data well defined and separated – Datatypes as complex as we need
Main points of the Object Oriented Programming ● Objects, classes, attributes, methods ... ● Reusability ● Data abstraction ● Encapsulation / data hiding ● Natural way of thinking ● Inheritance
Classes + Objects ● What is a Class ? – Concept – Data type – Template – .... ● Objects are instances of a class CLASS = Person OBJECT = Ruben ● We can define our own classes !
Examples of Classes PERSON ● Attributes ● First name ● Last name ● Mail address ● Birth date ● Methods ● Send a mail ● Ask if the person is over 18 BANK ACCOUNT ● Attributes ● PERSON ● Number ● Balance ● Methods ● Withdrawal ● Transfer ● Deposit
Examples of Objects PERSON ● John Smith ● Laura Ingells ● Marc van Gaal BANK ACCOUNT ● Account 12341234 ● Account 73763234 ● Account 87388234 All these objects have the ATTRIBUTES and METHODS defined by the class There is no any SEMANTIC in this, we defined the CLASS
Python: Classes and objects ● Define a class in python: ● Define a property for the class (indentation) ● Create an objet of this class ● Access to a property or method of the object
Python: Class Methods ● Are basically like a function but defined within a class ● They can be called through objects of the class ● ALL the class methods ALWAYS have as first parameter the object itself, and it's called self
Python: Manipulating data ● The class methods manipulate attributes of the objects ● These methods access to the data through the self parameter
Python: Type of Methods ● 'Getter' methods – To get some information (attribute) from the object ● 'Setter' methods – To set some information (attribute) to the object ● Processing methods – To do some stuff ● Special methods – Overloading methods – The __init__ method
Python: __init__ method ● Always with that name _ _ init _ _ it's the constructor of the class ● Used for define and initialize attributes ● It's called AUTOMATICALLY when we create the object
Python: __init__ method II ● Useful ! --> __init__ can get as many extra parameters as we need ● Exercise --> Create a method for the function call print_pet, that prints the data of the pet
Classes and objects. Advantages ● Code more clean, easy to reuse and debug and well structured ● Data encapsulation – You can make parts of your data “private” – Variables starting with __ are private ● Data abstraction – Data access through the methods, no matter how you store the data internally – Class Person: ● Attribute age as INTEGER or DATE ● Method is_over_18(...) --> True/False ● Reusability of code – Classes can be stored in one file and used used in N different files (import statement)
Classes and objects ● Highly recommended when you deal with complex data (and even with simple data) – You could represent the 'pet' as a tuple – Now you decide to include more attributes for your pet – Now you want to store also the information of the father, which is another PET – Now ... impossible to manage anymore :)
Classes and objects
Inheritance ● One class can inherit from another class (more than one) – General class --> parent / base class – Specialized class --> subclass ● Similar to hyperonym relation in WordNet :)
Inheritance II ● Subclasses can: – Reuse data/methods from base classes – Extend the functionality of base classes – Modify the behaviour of base classes ● Advantages of inheritance: – Reuse of code – Logic way of structure our classes – Code more clean and easy to debug – ....
Inheritance III ● How can we use inheritance in python: ● Our example: ● Both dog and pet are classes ● Dog is a subclass of pet ● All that a pet can do, also a dog can do it ● NOT all that a dog can do, a pet can do it
Inheritance IV. Exercise :) ● Extend the pet class with a method to print the name of the dog ● Create one object of 'pet' and one of 'dog' ● Which methods and data has any of the objects available?