← Python

While Loops

A while loop repeats its code block as long as its condition remains True

What it does: i starts at 0 and increments each loop. When i reaches 3, condition is False. while True runs forever — use break to exit when a condition is met. True never becomes False — the loop continues indefinitely. The condition is checked first — 5>0 is True, so 5 prints before decrementing. while, like if and for, requires a colon at the end of the line. The loop prints 1, 2, 3 then stops when i becomes 4. x decrements from 10 to 9 to 8. At 8 the condition fails, then prints 8. Repeats indented code as long as the condition is True.

Common mistakes: Code inside the while loop must be indented. Missing colon at the end of the while line.

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Learning

Duo

When does a while loop stop?

When the condition becomes FalseAfter 10 times

Matches

❌ while x < 10 x += 1

↓

Error: Missing colon after while

Applying

Meanings

Term

while

Meaning

Repeats indented code as long as the condition is True.

Practice

i = 0

Testing

Gaps

i < 5:

Check Answer

Spots

2while i < 5:

3print(i)

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Quick Questions

1. When does a while loop stop?

A. When the condition becomes False ✓

B. After 10 times

while keeps looping as long as its condition is True

2. i=0\nwhile i<3:\n print(i)\n i=i+1\nWhat prints?

A. 1, 2, 3

B. 0, 1, 2 ✓

i starts at 0 — it prints 0, 1, 2 then when i=3 the condition i<3 fails

3. What happens with while True: and no break?

A. The loop runs forever ✓

B. It runs once

True never becomes False — the loop continues indefinitely

4. What does the condition in a while loop check?

A. How many times to loop

B. Whether to keep looping ✓

The condition is checked before each iteration — if False, stop

5. count=5\nwhile count>0:\n print(count)\n count=count-1\nWhat prints first?

A. 5 ✓

B. 0

The condition is checked first — 5>0 is True, so 5 prints before decrementing

Match the Pairs

while x < 10 x += 1 → Error: Missing colon after while

i = 0 while i < 5: print(i) → Error: Infinite loop — never increments i

i = 0 while i < 3: i += 1 → Valid: Loop runs 3 times

while True: if done: break → Ok: Infinite loop with break

i = 1 while i <= 3: print(i) i += 1 → Output: 1 2 3

x = 10 while x > 8: x -= 1 print(x) → Output: 8

Key Term

while

Repeats indented code as long as the condition is True.~~Condition

Fill in the Blanks

1. i = 0 while i < 5: print(i) i = i + 1

2. i = 0 while i < 5: print(i) i = i + 1

3. i = 0 while i < 5: print(i) i = i + 1

4. i = 0 while i < 5: print(i) i = i + 1

5. count = 3 while count > 0: print(count) count = count - 1

Spot the Error

Question 1

A i = 0

B while i < 5:

C print(i)

D i = i + 1

Line C — Code inside the while loop must be indented

Question 2

A i = 0

B while i < 5

C print(i)

D i = i + 1

Line B — Missing colon at the end of the while line

Question 3

A i = 0

B while i < 5:

C print(i)

D # missing i = i + 1

Line C — Missing i = i + 1: the counter never increases, causing an infinite loop

Question 4

A i = 0

B While i < 5:

C print(i)

D i = i + 1

Line B — while must be lowercase: While is not valid Python

Question 5

A i = 0

B while i < 5:

C print(i)

D i = i + 1

E print('Done')

Line E — 'Done' is indented inside the loop it prints 5 times instead of once

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