__init__ method behavior in Python - Step-by-Step Execution

Concept Flow - __init__ method behavior

Create object instance

↓

Call __init__ method

↓

Initialize attributes

↓

Return new object

↓

Object ready to use

When you create a new object, Python calls __init__ to set up initial values inside the object.

Execution Sample

Python

class Dog:
    def __init__(self, name):
        self.name = name

d = Dog('Buddy')
print(d.name)

This code creates a Dog object with a name and prints the name.

Execution Table

Step	Action	Evaluation	Result
1	Create Dog object with 'Buddy'	Calls Dog.__init__(self, 'Buddy')	New Dog object created
2	Inside __init__, assign self.name = 'Buddy'	self.name set to 'Buddy'	Object attribute name initialized
3	Return from __init__	No return value (returns None)	Object fully initialized
4	Print d.name	Access attribute d.name	Output: Buddy

💡 Object created and initialized; program ends after printing name

Variable Tracker

Variable	Start	After Step 2	Final
self.name	undefined	'Buddy'	'Buddy'
d	undefined	Dog object created	Dog object with name='Buddy'

Key Moments - 2 Insights

Why do we use self.name inside __init__ instead of just name?

self.name stores the value inside the object so it can be used later; 'name' alone is just a temporary input. See execution_table step 2 where self.name is assigned.

Does __init__ return the new object?

__init__ does not return anything; Python creates the object first and then calls __init__ to initialize it. See execution_table step 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of self.name after step 2?

A None

B 'Buddy'

C undefined

D 'Dog'

💡 Hint

Check variable_tracker row for self.name after step 2

At which step does the __init__ method finish running?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

See execution_table where __init__ returns with no value

If we create Dog('Max') instead, what changes in the variable_tracker?

A d becomes None

B self.name stays 'Buddy'

C self.name becomes 'Max' instead of 'Buddy'

D No change at all

💡 Hint

Look at how self.name is assigned in step 2 and variable_tracker

Concept Snapshot

__init__ is a special method called when creating an object.
It sets up initial attributes using self.
self.name = value stores data inside the object.
__init__ does not return the object; Python does that.
Use __init__ to prepare your object for use.

Full Transcript

When you create a new object in Python, the __init__ method runs automatically. It sets up the object's attributes using the self keyword. For example, in the Dog class, __init__ takes a name and saves it as self.name. This means the object remembers its name. The __init__ method itself does not return the object; Python creates the object first and then calls __init__ to initialize it. After __init__ finishes, the object is ready to use. This process is shown step-by-step in the execution table and variable tracker.