IT, Programming, & Web Development › Forums › CS50’s Introduction to Computer Science by Harvard University on Edx › Week 6: Python › CS105: Introduction to Python by Saylor Academy › Unit 10: Object-Oriented Programming › Understanding the role of `self` in Python: How object instances manage their own data
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September 5, 2024 at 12:16 pm #3380
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In the method definition
def __init__(self, x, y):
,self
refers to the instance of the class that is being created. It is a reference to the current object and allows access to the object’s attributes and methods within the class.Why
self
is Needed:- Instance Reference: When you create an object of a class (e.g.,
my_object = SomeClass()
),self
is automatically passed to methods in that class. It acts as a reference to the specific instance of the class that is being operated on. Each instance has its own separateself
, which allows different objects to have their own attributes and methods. -
Assigning Attributes: In
__init__(self, x, y)
,self
allows you to assign instance variables likeself.x
andself.y
. These variables are tied to that particular instance, so when you access them later, you know that they belong to the specific object you created.
def __init__(self, x, y): self.x = x self.y = y
Here,
self.x
andself.y
become attributes of the instance, andx
andy
are the values passed during the object creation.- Different Instances, Different Data: Using
self
, you can create multiple instances of the class with different values for the attributes. Each instance will store its own values separately, thanks toself
.
Example:
class Point: def __init__(self, x, y): self.x = x self.y = y # Creating two instances of the Point class point1 = Point(2, 3) point2 = Point(5, 7) print(point1.x, point1.y) # Output: 2, 3 print(point2.x, point2.y) # Output: 5, 7
Here:
–self.x = x
andself.y = y
allow the instancepoint1
to store its ownx
andy
values, independent ofpoint2
.
–self
is required because it tells Python that thex
andy
attributes belong to the specific instance (point1
orpoint2
), not the class itself or some other instance.Summary:
self
is a reference to the current instance of the class.- It allows each instance of a class to have its own attributes and methods.
- Without
self
, Python wouldn’t know which object’s data you are working with inside the class methods.
- Instance Reference: When you create an object of a class (e.g.,
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