Adding custom attributes in Python - Step-by-Step Execution

Concept Flow - Adding custom attributes

Create object

↓

Add custom attribute

↓

Access or modify attribute

↓

Use attribute in code

↓

End

This flow shows how to create an object, add a custom attribute to it, then access or modify that attribute during program execution.

Execution Sample

Python

class Car:
    pass

car = Car()
car.color = 'red'
print(car.color)

This code creates an empty class Car, adds a custom attribute 'color' to an instance, and prints its value.

Execution Table

Step	Action	Object State	Output
1	Define class Car (empty)	Car class created, no attributes
2	Create instance car = Car()	car is an instance of Car, no attributes yet
3	Add attribute car.color = 'red'	car now has attribute 'color' with value 'red'
4	Print car.color	car.color is 'red'	red
5	End of program	No changes

💡 Program ends after printing the custom attribute value.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
car	undefined	Car instance with no attributes	Car instance with color='red'	Same	Same
car.color	undefined	undefined	'red'	'red'	'red'

Key Moments - 2 Insights

Why can we add an attribute to an object that was not defined in the class?

In Python, objects can have attributes added dynamically after creation, as shown in step 3 of the execution_table where 'color' is added to 'car' even though Car class is empty.

What happens if we try to access an attribute that was never added?

Trying to access a non-existent attribute causes an AttributeError. Here, we only access 'car.color' after adding it in step 3, so no error occurs.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what attribute does 'car' have?

A 'color' with value 'red'

B No attributes

C 'color' with value 'blue'

D 'speed' with value 100

💡 Hint

Check the 'Object State' column at step 3 in the execution_table.

At which step is the attribute 'color' first created on 'car'?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look for when 'car.color' appears in the variable_tracker and execution_table.

If we tried to print 'car.speed' instead of 'car.color', what would happen?

A It would print 'speed' value if set before

B It would print 'null'

C It would cause an error because 'speed' was never added

D It would print an empty string

💡 Hint

Refer to key_moments about accessing attributes not added to the object.

Concept Snapshot

Adding custom attributes in Python:
- Create an object from a class
- Add attribute by assignment: obj.attr = value
- Access attribute by obj.attr
- Attributes can be added anytime after object creation
- Accessing missing attributes causes errors

Full Transcript

This example shows how to add custom attributes to Python objects. First, we define an empty class Car. Then, we create an instance called car. Next, we add a new attribute 'color' to car by assigning car.color = 'red'. Finally, we print car.color which outputs 'red'. Python allows adding attributes dynamically to objects after they are created. Trying to access an attribute that was never added will cause an error. This is a simple way to customize objects without changing the class definition.