Hey everyone in this tutorial I want to share what I learned about self in python, As far as I know, this is one of the things that most of the beginners like me have a problem understanding in OOP and Classes!
I'm here to write like a beginner(Simple) not a Pro(difficult) to give you a light and show you how cool it is when you understand what does exactly self do behind the scene, so No more pain when you want to create a class!
so let's dive into it and improve our coding skills:
First, you need to know about two things:
Method: A function which is associated with a class
Attributes: Some data that is related to a class
So, we want to have a Class(Object) for our College or University and want to represent students with python codes!
In this cause we can have class cause every student can have some methods and attributed like age, name, email, loan, pay and etc.
π‘ Note: Make sure you are starting your class name with an upper case letter. (It's a convention!) like:
class Name:
pass
Let's create our first class >>> :
class Student:
pass
- What is the Differences between class and instance of a class?
A class is like a blueprint and a sample for creating instances, and every student that we'll create would be an instance of our Student() class and every instance is unique! (It means they are in different locations in memory).
Take a look at this example below:
class Student:
pass
first_student = Student()
second_student = Student()
In this case first_student and second_student are the instances of our Student() class.
*What did I mean when I said every instance is unique?
Let's print our two instances and see what will happen...
print(first_student, second_student)
Output:
>>> <__main__.Student object at 0x7f68e60b0820>
<__main__.Student object at 0x7f68e60b0d30>
as you can see they are in different locations in Memory(b0820 and b0d30).
I want to show you how hard it is if you code instance variable manually without using class!
class Student:
pass
first_student = Student()
second_student = Student()
first_student.first_name = "James"
first_student.last_name = "White"
first_student.email = "James.White@collegename.com"
first_student.age = 21
first_student.loan = 1000
second_student.first_name = "Leo"
second_student.second_name = "Ledger"
second_student.email = "Leo.Ledger@collegename.com"
second_student.age = 45
second_student.loan = 2400
So here we have 5 attributes that are unique to the instances.
let's look at this example:
print(first_student.age, second_student.age)
Output:
>>> 21 45
But as you saw we wrote 10 lines of code for only 5 attributes, there's another way to do it.
If we want to do all of these tasks automatically and save your time we have to use a special method which is called def __init__ method!(which means initialize).
π‘ Note: It's a convention to use self when you want to call instances in Classes.
After self you can define your arguments .
Inside of our def __init__ method
class Student:
def __init__(self, first_name, last_name, age, loan):
self.first_name = first_name
self.last_name = last_name
self.age = age
self.loan = loan
self.email = first_name + last_name + "@collegename.com"
What does "self" do in python class?
If we compare the above examples, we created instance variables in two ways:
- Manually
- Automatically let's take a look at the
first_namevariable when we created Manually:
first_student.first_name = "James"
and Automatically:
class Student:
def __init__(self, first_name):
self.first_name = first_name
and Comparing both of them...
Manually:
first_student.first_name = "James"
VS
Automatically:
def __init__(self, first_name):
self.first_name = first_name
As you can see, the self exactly behave like an instance which means
self is equal to first_student.
So when we call self in our Classes it behaves like instances but in an automatic way!
So when we pass self in our def __init__ method it will replace self with instances that you define.
Take a look at this example to understand what do I mean:
class Student:
def __init__(self, first_name, last_name, age, loan):
self.first_name = first_name
self.last_name = last_name
self.age = age
self.loan = loan
self.email = first_name + last_name + "@collegename.com"
first_student = Student("Muhammad", "Khanjani", 22, 2000)
print(first_student.first_name)
when we write:
first_student = Student("Muhammad", "Khanjani", 22, 2000)
print(first_student.name)
Output:
Muhammad
The __init__ method will be run automatically, so the first student will be passed as self in our class and will set all of the attributes that we defined in Student("Muhammad", "Khanjani", 22, 2000)!
so, for the other:
Manually:
self.last_name = last_name
self.age = age
self.loan = loan
self.email = first_name + last_name + "@collegename.com"
VS
Automatically:
first_student.last_name = "White"
first_student.email = "James.White@collegename.com"
first_student.age = 21
first_student.loan = 1000
So you can think self exactly as an instance in python class!
Complete Comparison between Manually and Automatically(using self and init method!):
class Employee:
def __init__(self, first, last, pay):
self.firstname = first
self.lastname = last
self.pay = pay
self.email = first + "." + last + "@banji.com"
def fullname(self):
return f"{self.firstname} {self.lastname}"
emp_1 = Employee("MuhammadHussein", "Khanjani", 5000)
emp_2 = Employee("Farshid", "Keshavaz", 2000)
print(emp_1.firstname)
print(emp_2.email)
VS
class Employee2:
pass
emp_1 = Employee2()
emp_2 = Employee2()
emp_1.firstname = 'Walter'
emp_1.lastname = 'White'
emp_1.full_name = emp_1.firstname + emp_1.lastname
emp_1.email = 'Walter.White@gmail.com'
emp_1.pay = 50000
emp_2.firstname = 'Jesse'
emp_2.lastname = 'Pinkman'
emp_2.full_name = emp_2.firstname + emp_2.lastname
emp_2.email = 'Jesse.Pinkman@gmail.com'
emp_2.pay = 2000
print(emp_1.firstname)
print(emp_2.email)
This is the first part of self in python and classes, I don't want to write too long, cause it will be tedious for beginners like me!
I hope you get the purposes of the self in classes, but if you need more explanation and you think you can write more clear and adding something to this post just let me know and leave a comment below, share your knowledge and point of view with us.
Thank you for reading my post.
Keep Moving Forward γ
Enjoy Your Journey π
Code with π
π π π π π
Top comments (6)
Cleared things up a lot. Thank you !
Tnx for reading my post :)
GOOD LUCK
HAPPY CODING
BANJI
Cool good read.
what a nice description of self
I just couldn't find myself as a student there : )))))
Keep moving forward and Erupt like a volcano bro π
Tmx dude, I'm writing this kind of posts in the easiest way.
Cause I'm a hard learner, I wan explain in a way that most of the beginners could understand it.
That's why my articles are PURE gold.
Take advantage of them broβ€οΈ
Tnx Pavel ;)