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Loops: while and do-while loops

Following our exploration of Loops: for loops (Part 2), this article introduces another type of loop: the while loop. We'll also see how to simulate a do-while loop, which is not a native feature of Python.

📚 Prerequisites​

A basic understanding of Python loops and conditional statements.

🎯 Article Outline: What You'll Master​

In this article, you will learn:

  • ✅ The syntax of the while loop.
  • ✅ How to use while loops to repeat code based on a condition.
  • ✅ How to create infinite loops and how to break out of them.
  • ✅ How to simulate a do-while loop in Python.

🧠 Section 1: The while Loop​

The while loop repeatedly executes a block of code as long as a given condition is True.

Syntax:

while condition:
    # code to be executed
  • condition: A boolean expression that is evaluated before each iteration.

Example:

count = 0
while count < 5:
    print(count)
    count += 1

In this example, the loop will continue as long as count is less than 5. It's crucial to have a way to make the condition False at some point, otherwise you'll have an infinite loop.

💻 Section 2: Infinite Loops and break​

An infinite loop is a loop that runs forever because its condition always remains True. You can use the break statement to exit a loop at any time.

while True:
    user_input = input("Enter 'quit' to exit: ")
    if user_input == 'quit':
        break
    print(f"You entered: {user_input}")

🛠️ Section 3: Simulating a do-while Loop​

Python doesn't have a built-in do-while loop. A do-while loop is a loop that executes the code block at least once, and then checks the condition at the end of the loop.

You can simulate a do-while loop using a while True loop with a break statement at the end:

while True:
    # code to be executed at least once
    user_input = input("Enter a number: ")
    number = int(user_input)
    print(f"The square of your number is {number ** 2}")

    # check the condition at the end
    if number < 0:
        break

💡 Conclusion & Key Takeaways​

You've now learned how to use while loops to create more flexible and powerful programs.

Let's summarize the key takeaways:

  • while Loop: Repeats a block of code as long as a condition is True.
  • Infinite Loops: Can be created with while True and exited with break.
  • do-while Loop: Not a native feature of Python, but can be simulated with while True and break.

Challenge Yourself: Write a script that simulates a simple guessing game. The script should generate a random number between 1 and 10, and then ask the user to guess the number. The script should continue to ask for guesses until the user guesses the correct number.

➡️ Next Steps​

In the next article, we'll learn about "Loops: foreach loops".

Happy coding!

Glossary (Python Terms)​

  • while loop: A control flow statement that allows code to be executed repeatedly based on a given boolean condition.
  • Infinite loop: A loop that continues to execute forever.
  • do-while loop: A loop that executes a block of code at least once, and then repeatedly executes the block as long as a condition is true.

Further Reading (Python Resources)​