Python while Loop

What is a while loop in Python?

A while loop in Python is a control flow statement used to repeatedly execute a block of code as long as a given condition is True.

It is useful when:

• The number of iterations is not known in advance
• You want to loop based on a condition

Syntax of while Loop in Python:

while condition:
    # code block to execute repeatedly

• The loop continues as long as the condition is True
• Once the condition becomes False, the loop stops

Example 1: Basic while Loop

count = 1

while count <= 5:
    print("Count is:", count)
    count += 1

Output:

Count is: 1
Count is: 2
Count is: 3
Count is: 4
Count is: 5

Explanation:

• The loop runs as long as count <= 5
• count is incremented in each iteration

Example 2: while Loop with else

x = 3

while x > 0:
    print("x =", x)
    x -= 1
else:
    print("Loop completed.")

Output:

x = 3
x = 2
x = 1
Loop completed.

Explanation:

The else block runs after the while condition becomes False

Example 3: Infinite while Loop

while True:
    print("This will run forever")
    break  # Stops after first iteration

Output:

This will run forever

Explanation:

Use break to avoid an infinite loop when using while True

Real-World Example: Password Prompt

password = ""

while password != "python123":
    password = input("Enter password: ")

print("Access Granted")

Explanation:

The loop keeps asking for a password until the correct one is entered

Useful Keywords with while Loop

Common Mistakes to Avoid

• Forgetting to update the loop variable - leads to infinite loop
• Always ensure the condition can become False
• Don't forget indentation in Python