Python Programs

Share with a Friend

Python Programs - Recursion Functions

Recursive function for Fibonacci - Python Program

Example 1 :

def fibonacci(n):
    """Return n-th Fibonacci number using recursion."""
    if n <= 1:
        return n
    return fibonacci(n-1) + fibonacci(n-2)

print([fibonacci(i) for i in range(7)])

 
OUTPUT  :
[0, 1, 1, 2, 3, 5, 8]
 

Example 2 : Advanced Program

def fibonacci_recursive(n):
    """
    Calculates the nth Fibonacci number recursively.

    Args:
        n: The index of the Fibonacci number to calculate (non-negative integer).

    Returns:
        The nth Fibonacci number.
    """
    if n <= 1:
        return n
    else:
        return fibonacci_recursive(n - 1) + fibonacci_recursive(n - 2)

# Get the number of terms from the user
num_terms = int(input("Enter the number of Fibonacci terms to generate: "))

if num_terms <= 0:
    print("Please enter a positive integer.")
else:
    print("Fibonacci sequence:")
    for i in range(num_terms):
        print(fibonacci_recursive(i), end=" ")
    print() # For a newline at the end

 
OUTPUT 1 :
Enter the number of Fibonacci terms to generate: 5
Fibonacci sequence:
0 1 1 2 3  


OUTPUT 2 :
Enter the number of Fibonacci terms to generate: 10
Fibonacci sequence:
0 1 1 2 3 5 8 13 21 34 

Explanation:

fibonacci_recursive(n) Function:

• Base Case:The if n <= 1: condition handles the base cases of the recursion. The first two Fibonacci numbers are defined as 0 and 1. If n is 0 or 1, the function directly returns n.
• Recursive Case:The else: block handles the recursive step. For any n greater than 1, the function calculates the nth Fibonacci number by recursively calling itself to get the (n-1) th and (n-2) th Fibonacci numbers and summing them.

User Input and Output:

• The program prompts the user to enter the desired number of Fibonacci terms.
• It includes a check to ensure the input is a positive integer.
• A forloop iterates from 0 up to num_terms - 1, calling fibonacci_recursive(i) for each iteration to calculate and print the corresponding Fibonacci number.
• end=" "is used in the print statement to keep the numbers on the same line, separated by spaces.