Python while Loop

In control structures, such as the while loop, the execution of code can be repeated for as long as the condition is true. It is one of the fundamental control structures that let Python do repetitive work.

Syntax of the while loop

while condition:
  # Code to execute as long as the condition is True

Key Components

1. condition:

• A condition is a logical expression with an outcome of either True or False.
• While this condition is true, the loop will continue executing.

2. Body of the while Loop:

• A series of commands that are executed repeatedly.
• Indentation is used to guide execution.

3. Loop Termination:

• The loop would stop executing once the condition gets False.

Flowchart

1. Evaluate the condition:

• If True, then execute the body of the loop.
• If False, then exit the loop and move to the next line of code.

2. After every iteration, the condition is checked again.

Example 1: Simple Counter

count = 0

while count < 5:
   print("Count is:", count)
   count += 1   # Increment count to avoid infinite loop

Output:

Count is: 0
Count is: 1
Count is: 2
Count is: 3
Count is: 4

Explanation:

• It starts from count = 0.
• The loop condition count < 5 is True, so it executes the loop body.
• The value of count is incremented by 1 in each iteration.
• The moment the count reaches 5, the condition turns False and the loop exists.

Potential Issues

Infinite Loops:

• If the condition is always True, then the loop will never stop.
• Example:

           while True:
                print("This will run forever!")

• To prevent this, ensure the condition eventually becomes False.

Forgotten Updates:

• Failure to change variables associated with the condition may lead to infinite loops.
• Always ensure that the condition is updated appropriately within the loop.

Example 2: Using break to Exit the Loop

i = 0

while i < 10:
   print("Number:", i)
   if i == 5:
       break  # Exit the loop when i is 5
   i += 1

Output:

Number: 0
Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Example 3: Using continue to Skip an Iteration

i = 0

while i < 5:
   i += 1
   if i == 3:
       continue  # Skip the rest of the code for this iteration
   print("Number:", i)

Output:

Number: 1
Number: 2
Number: 4
Number: 5

Explanation:

• The continue statement skips the rest of the loop body and proceeds to the next iteration.

Example 4: Using else with a while Loop

x = 0

while x < 3:
   print("Value of x:", x)
   x += 1
else:
   print("Loop finished")

Output:

Value of x: 0
Value of x: 1
Value of x: 2
Loop finished

Real -World Use Case: User Input

password = ""

while password != "1234":
   password = input("Enter the password: ")
   if password == "1234":
      print("Access granted")
   else:
      print("Wrong password, try again")

Key Takeaways

• The while loop is useful for repeating tasks when the number of iterations is not known beforehand.
• Always ensure the condition eventually becomes False to avoid infinite loops.
• Use break to get out of the loop early and continue to skip parts of the loop.