Identity operators (is, is not) in Python - Step-by-Step Execution

Concept Flow - Identity operators (is, is not)

Start

↓

Evaluate x and y

↓

Check: x is y?

Yes→Execute 'is' branch

No↓

Check: x is not y?

Yes→Execute 'is not' branch

No↓

End

The program compares two variables to see if they point to the same object using 'is' or 'is not' and executes code accordingly.

Execution Sample

Python

a = [1, 2, 3]
b = a
c = [1, 2, 3]
print(a is b)
print(a is c)
print(a is not c)

This code checks if variables refer to the same object using 'is' and 'is not' operators.

Execution Table

Step	Expression	Evaluation	Result	Output
1	a = [1, 2, 3]	Create list object	a points to list1
2	b = a	Assign b to same object as a	b points to list1
3	c = [1, 2, 3]	Create new list object	c points to list2
4	a is b	Compare if a and b point to same object	True	True
5	a is c	Compare if a and c point to same object	False	False
6	a is not c	Compare if a and c do NOT point to same object	True	True

💡 All expressions evaluated; program ends after printing results.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
a	undefined	list1	list1	list1	list1
b	undefined	undefined	list1	list1	list1
c	undefined	undefined	undefined	list2	list2

Key Moments - 2 Insights

Why does 'a is b' return True but 'a is c' return False even though a and c have the same list values?

'a is b' is True because b points to the exact same list object as a (see step 2 and 4). 'a is c' is False because c is a new list object with the same values but different identity (step 3 and 5).

What does 'is not' check compared to 'is'?

'is not' checks if two variables do NOT point to the same object. In step 6, 'a is not c' is True because a and c are different objects.

Visual Quiz - 3 Questions

Look at the execution table, what is the result of 'a is b' at step 4?

A Error

B False

C True

D None

💡 Hint

Check the 'Result' column in row for step 4 in the execution_table.

At which step does the variable 'c' get assigned a new list object?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at the 'Expression' and 'Evaluation' columns for when 'c' is assigned in the execution_table.

If we changed 'b = a' to 'b = [1, 2, 3]', what would 'a is b' evaluate to at step 4?

A False

B True

C Error

D None

💡 Hint

Refer to variable_tracker to see that 'b' would point to a new object, so 'a is b' would be False.

Concept Snapshot

Identity operators check if two variables point to the same object.
Use 'is' to test if they are the same object.
Use 'is not' to test if they are different objects.
They compare object identity, not values.
Example: a is b returns True if a and b point to the same object.

Full Transcript

This lesson shows how Python's identity operators 'is' and 'is not' work by comparing if two variables point to the same object in memory. We assign lists to variables and check if they are identical objects. The 'is' operator returns True if both variables point to the same object, and False otherwise. The 'is not' operator returns True if they point to different objects. We traced each step, showing variable assignments and comparisons, and explained why two lists with the same values can be different objects. This helps beginners understand the difference between object identity and equality.