Fibonacci Sequence Function (Python)

def fibonacci(n):
    # Handle the base cases. These are also terms that have to be followed by the code.
    if n <= 0:
        return "Input should be a positive integer."
    elif n == 1:
        return 0
    elif n == 2:
        return 1
    
    # Start with the first two Fibonacci numbers
    fib_1, fib_2 = 0, 1
    
    # Use an iterative approach to find the nth Fibonacci number. This is the function that models the Fibonacci sequence.
    for i in range(3, n+1):
        fib_next = fib_1 + fib_2
        fib_1, fib_2 = fib_2, fib_next
    
    return fib_2

n = 9  
result = fibonacci(n)
print(f"The {n}th Fibonacci number is: {result}")

The 9th Fibonacci number is: 21