When to use while loops vs recursion

Question

I am a beginner and I am beginning to learn about 'while' statement loops to perform iteration. However, earlier on I learned about 'if/else' statements and how one can perform recursion using if/else by returning a variable as well. Here's a simple countdown function using while statement:

def countdown(n):
    while n > 0:
        print(n)
        n = n-1
    print('Blast off!')

And for comparison, here is a simple countdown function using if/else and recursion.

def countdown(n):
    if n > 0:
        print(n)
        return countdown(n-1)
    elif n < 0:
        return None
    else:
        print('Blast off!')
        return

As you can see, the two functions do almost exactly the same thing, with the only difference being that the if/else statement accounts for a case where n < 0 and returns a None value, while the 'while' statement simply omits the loop and prints 'Blast off!' even if n < 0 anyway. (If there is a way to factor this in the while statement, I would love to learn, do suggest!)

My question is, seeing how the same thing can be done in if/else statements and while statements and vice versa, I would like to know a case where they are clearly differentiated and one is clearly preferable to the other. Is there a subtle conceptual difference between the two types of statements that I am missing, or are they interchangeable in usage?

Answer 1

You are actually right, the logic behind is the same and you can also apply while loop for e.g. Fibonacci sequence. Just the notation of recursion is usually shorter and more elegant.

Your code can be even simplified a bit and then you see that your solutions are kind of similar:

While loop:

def countdown(n):
    while n > 0: # Step 1 -> check
        print(n)
        n = n-1 # Step 2  -> recursive call in while loop
    print('Blast off!') # Step 3 -> end ensured by Step 1

Recursion:

def countdown(n):
    if n > 0: # Step 1 -> check
        print(n)  
        return countdown(n-1) # Step 2 -> recursive call of the countdown()
    else:
        print('Blast off!') # Step 3 -> end ensured by Step 1

Significant is that action n-1. You recursively act on a variable or object (Step 2) as long as your condition related to that variable/object is valid (Step 1).