Iteration using range() in Python - Step-by-Step Execution

Concept Flow - Iteration using range()

Start: i = 0

↓

Check: i < stop?

No→Exit loop

Yes↓

Execute loop body

↓

Update: i = i + 1

↩Back to Check

The loop starts with i at 0, checks if i is less than stop value, runs the loop body if yes, then increases i by 1 and repeats until the condition is false.

Execution Sample

Python

for i in range(3):
    print(i)

This code prints numbers 0, 1, and 2 by looping over range(3).

Execution Table

Iteration	i value	Condition (i < 3)	Action	Output
1	0	True	Print i	0
2	1	True	Print i	1
3	2	True	Print i	2
4	3	False	Exit loop

💡 i reaches 3, condition 3 < 3 is False, loop ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	0 (initial)	1	2	3	3 (loop ends)

Key Moments - 3 Insights

Why does the loop stop when i equals 3?

Because the condition i < 3 becomes False at i = 3, so the loop exits as shown in execution_table row 4.

Does the loop include the stop value 3 in the output?

No, the loop runs while i is less than 3, so it stops before reaching 3, as seen in the outputs 0, 1, 2.

What happens if range(3) is changed to range(5)?

The loop will run 5 times with i from 0 to 4, increasing the number of rows in execution_table accordingly.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i at iteration 2?

A 0

B 1

C 2

D 3

💡 Hint

Check the 'i value' column in execution_table row for iteration 2.

At which iteration does the condition become false and the loop stops?

A 4

B 3

C 2

D 1

💡 Hint

Look at the 'Condition' and 'Action' columns in execution_table to find when the loop exits.

If we change range(3) to range(2), how many times will the loop run?

A 1 time

B 3 times

C 2 times

D 0 times

💡 Hint

Refer to variable_tracker to see how i changes with different range values.

Concept Snapshot

for i in range(stop):
    # loop body

- i starts at 0
- runs while i < stop
- increments i by 1 each loop
- stop value is NOT included
- prints 0 to stop-1

Full Transcript

This visual trace shows how a for loop with range(stop) works in Python. The loop starts with i at 0 and runs as long as i is less than the stop value. Each iteration prints the current i and then increases i by 1. When i reaches the stop value, the condition becomes false and the loop ends. The execution table tracks each iteration's i value, condition check, action, and output. The variable tracker shows how i changes step by step. Key moments clarify why the loop stops before reaching the stop value and what happens if the range changes. The quiz tests understanding of i values and loop stopping conditions.