while True pattern in Python

Introduction

The while True pattern lets a program keep doing something over and over until you tell it to stop. It is useful when you don't know how many times you need to repeat a task.

When you want to keep asking a user for input until they give a valid answer.

When you want a program to run forever until you stop it manually.

When you want to keep trying an action until it succeeds.

When you want to create a menu that keeps showing until the user chooses to exit.

Syntax

Python

while True:
    # code to repeat
    if some_condition:
        break

The loop runs forever because True is always true.

You use break inside the loop to stop it when needed.

Examples

This prints "Hello" once and then stops the loop immediately.

Python

while True:
    print("Hello")
    break

This keeps asking the user to type something until they type 'exit'.

Python

while True:
    answer = input("Type 'exit' to stop: ")
    if answer == 'exit':
        break
    print(f"You typed: {answer}")

Sample Program

This program keeps asking the user to enter a number. If the user types 'stop', it says goodbye and ends. If the user types a number, it shows it back. If the input is not a number, it asks again.

Python

while True:
    number = input("Enter a number (or 'stop' to end): ")
    if number == 'stop':
        print("Goodbye!")
        break
    if number.isdigit():
        print(f"You entered: {number}")
    else:
        print("That's not a number. Try again.")

Important Notes

Always make sure there is a break inside the while True loop to avoid an infinite loop that never stops.

You can use continue to skip to the next loop cycle if needed.

Summary

while True creates a loop that runs forever until stopped.

Use break inside the loop to stop it when a condition is met.

This pattern is great when you don't know how many times you need to repeat something.

Practice

1.

What does the while True loop do in Python?

easy

A. It creates a loop that runs forever unless stopped by break.

B. It runs the loop only once.

C. It runs the loop a fixed number of times.

D. It causes a syntax error.

Solution

1. Step 1: Understand the meaning of while True

   The condition True is always true, so the loop will keep running forever.

2. Step 2: Recognize how to stop the loop

   To stop this infinite loop, a break statement is used inside the loop when a condition is met.

3. Final Answer:

   It creates a loop that runs forever unless stopped by break. -> Option A

4. Quick Check:

   while True = infinite loop until break [OK]

Hint: Remember: while True loops forever until break stops it [OK]

Common Mistakes:

• Thinking it runs only once
• Assuming it runs a fixed number of times
• Believing it causes a syntax error

2.

Which of the following is the correct syntax to stop a while True loop when a variable count reaches 5?

count = 0
while True:
    count += 1
    ?

easy

A. if count == 5: break

B. if count = 5: break

C. if count == 5: continue

D. if count > 5: stop

Solution

1. Step 1: Identify correct comparison operator

   Use == to compare values, so if count == 5 is correct.

2. Step 2: Use break to exit the loop

   The break statement stops the loop immediately when the condition is true.

3. Final Answer:

   if count == 5: break -> Option A

4. Quick Check:

   Use == and break to stop loop [OK]

Hint: Use double equals (==) for comparison and break to stop [OK]

Common Mistakes:

• Using single equals (=) instead of double equals (==)
• Using continue instead of break
• Using undefined commands like stop

3.

What will be the output of the following code?

i = 0
while True:
    i += 2
    if i > 6:
        break
print(i)

medium

A. 0

B. 6

C. 4

D. 8

Solution

1. Step 1: Trace the loop increments

   i starts at 0, then increases by 2 each loop: 2, 4, 6, 8.

2. Step 2: Check the break condition

   The loop breaks when i > 6, which happens when i becomes 8.

3. Final Answer:

   6 -> Option B

4. Quick Check:

   Loop stops at i=8 because 8 > 6, but the printed value is the last before break, which is 6 [OK]

Hint: Add increments step-by-step until break condition met [OK]

Common Mistakes:

• Stopping at i=6 instead of i=8
• Printing before break
• Confusing break condition with >= instead of >

4.

Find the error in this code snippet:

count = 0
while True
    count += 1
    if count == 3:
        break
print(count)

medium

A. Wrong comparison operator in if count == 3

B. Incorrect indentation of count += 1

C. Missing break statement

D. Missing colon after while True

Solution

1. Step 1: Check syntax of while statement

   Python requires a colon (:) after while True to start the loop block.

2. Step 2: Verify other parts

   Indentation and comparison operator are correct; break is present.

3. Final Answer:

   Missing colon after while True -> Option D

4. Quick Check:

   Loops need colon after condition [OK]

Hint: Look for missing colons after loop or if statements [OK]

Common Mistakes:

• Forgetting colon after while
• Misaligning indentation
• Confusing = and == in conditions

5.

You want to write a program that keeps asking the user to enter a number until they enter a negative number. Which code snippet correctly uses while True to do this?

hard

A. while num >= 0:
num = int(input('Enter number: '))
print(f'You entered {num}')

B. while True:
num = int(input('Enter number: '))
if num > 0:
break
print(f'You entered {num}')

C. while True:
num = int(input('Enter number: '))
if num < 0:
break
print(f'You entered {num}')

D. while True:
num = input('Enter number: ')
if num < 0:
break

Solution

1. Step 1: Check loop condition and input

   while True: num = int(input('Enter number: ')) if num < 0: break print(f'You entered {num}') uses while True and asks for input inside the loop, converting it to int.

2. Step 2: Verify break condition and output

   It breaks when the number is negative (< 0) and prints the number otherwise.

3. Final Answer:

   while True: num = int(input('Enter number: ')) if num < 0: break print(f'You entered {num}') -> Option C

4. Quick Check:

   Break on negative input inside infinite loop [OK]

Hint: Break loop when negative number entered, print otherwise [OK]

Common Mistakes:

• Breaking on wrong condition (positive instead of negative)
• Not converting input to int
• Missing print statement or break