python classes

Python Classes/Objects

Python is an object oriented programming language.

Almost everything in Python is an object, with its properties and methods.

A Class is like an object constructor, or a "blueprint" for creating objects.

Create a Class

To create a class, use the keyword class:

Example

Create a class named MyClass, with a property named x:



class MyClass:  x = 5

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Example

Create a class named MyClass, with a property named x:

Create Object

Now we can use the class named MyClass to create objects:

Example

Create an object named p1, and print the value of x:



p1 = MyClass()print(p1.x)

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Example

Create an object named p1, and print the value of x:

The __init__() Function

The examples above are classes and objects in their simplest form, and are

not really useful in real life applications.

To understand the meaning of classes we have to understand the built-in __init__()

function.

All classes have a function called __init__(), which is always executed when

the class is being initiated.

Use the __init__() function to assign values to object properties, or other

operations that are necessary to do when the object

is being created:

Example

Create a class named Person, use the __init__() function to assign values

for name and age:



class Person:  def __init__(self, name, age):   

self.name = name    self.age = agep1 = Person("John",

36)

print(p1.name)print(p1.age)

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Example

Create a class named Person, use the __init__() function to assign values

for name and age:

Note: The __init__() function is called automatically every time the class is being used to create a new object.

Object Methods

Objects can also contain methods. Methods in objects are functions that

belong to the object.

Let us create a method in the Person class:

Example

Insert a function that prints a greeting, and execute it on the p1 object:



class Person:  def __init__(self, name, age):   

self.name = name    self.age = age  def myfunc(self):   

print("Hello my name is " + self.name)p1 = Person("John",

36)p1.myfunc()

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Example

Insert a function that prints a greeting, and execute it on the p1 object:

Note: The self parameter

is a reference to the current instance of the class, and is used to access variables that belong to the class.

The self Parameter

The self parameter is a reference to the

current instance of the class, and is used to access variables that belongs to the class.

It does not have to be named self , you can

call it whatever you like, but it has to be the first parameter of any function

in the class:

Example

Use the words mysillyobject and abc instead of self:



class Person:  def __init__(mysillyobject, name, age):   

mysillyobject.name = name    mysillyobject.age = age  def myfunc(abc):   

print("Hello my name is " + abc.name)p1 = Person("John",

36)p1.myfunc()

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Example

Use the words mysillyobject and abc instead of self:

Modify Object Properties

You can modify properties on objects like this:

Example

Set the age of p1 to 40:



p1.age = 40

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Example

Set the age of p1 to 40:

Delete Object Properties

You can delete properties on objects by using the

del keyword:

Example

Delete the age property from the p1 object:



del p1.age

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Example

Delete the age property from the p1 object:

Delete Objects

You can delete objects by using the del keyword:

Example

Delete the p1 object:



del p1

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Example

Delete the p1 object:

The pass Statement

class definitions cannot be empty, but if

you for some reason have a class definition with no content, put in the pass statement to avoid getting an error.

Example



class Person:  pass

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Example

Test Yourself With Exercises

Exercise:

Create a class named MyClass:

Start the Exercise