While–else behavior in Python - Step-by-Step Execution

Concept Flow - While–else behavior

Start: Initialize condition

↓

Check condition

↓

Execute body

↓

Update condition

↩Back to Check condition

The while loop runs as long as the condition is true. If it ends normally (condition false), the else block runs. If the loop exits early (break), else is skipped.

Execution Sample

Python

i = 0
while i < 3:
    print(i)
    i += 1
else:
    print('Done')

Counts from 0 to 2, then prints 'Done' after the loop finishes normally.

Execution Table

Step	i	Condition (i < 3)	Action	Output
1	0	True	Print 0, i = i + 1	0
2	1	True	Print 1, i = i + 1	1
3	2	True	Print 2, i = i + 1	2
4	3	False	Exit loop, run else	Done
5	-	-	End	-

💡 i reaches 3, condition 3 < 3 is False, loop ends normally, else block runs

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	0	1	2	3	3

Key Moments - 2 Insights

Why does the else block run after the while loop?

Because the loop ended normally when the condition became False (see execution_table step 4). The else runs only if no break interrupts the loop.

What happens if we add a break inside the loop?

If break runs, the loop exits immediately and the else block does NOT run. This is because else runs only on normal loop completion.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i at step 3?

A 2

B 3

C 1

D 0

💡 Hint

Check the 'i' column at step 3 in the execution_table.

At which step does the condition become False and the else block runs?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Condition' and 'Action' columns in execution_table for when condition is False and else runs.

If we add 'if i == 1: break' inside the loop, what happens to the else block?

A It runs before the loop

B It runs after the loop

C It does not run

D It runs twice

💡 Hint

Recall key_moments about break skipping the else block.

Concept Snapshot

while condition:
    # loop body
else:
    # runs if loop ends normally (no break)

- else runs only if while condition becomes False
- else skipped if break exits loop early
- useful for post-loop actions when no early exit

Full Transcript

This visual trace shows how a while loop with an else block works in Python. The loop runs while the condition is true, updating variable i each time. When i reaches 3, the condition becomes false, so the loop ends normally and the else block runs, printing 'Done'. If the loop had a break statement, the else block would not run. The variable tracker shows how i changes each step. The key moments clarify why else runs only on normal loop completion. The quiz questions help check understanding of the loop steps and else behavior.