Fibonacci Numbers using Python

Fibonacci sequence is a series of numbers where each number is the sum of two preceding numbers. The sequence is given by:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144 and so on

We can generate above Fibonacci sequence programmatically with or without recursion. 

Fibonacci series without recursion:

Below function prints x Fibonacci numbers starting from 0. 

def fib(x):
    a = 0
    b = 1
    if x < 1:
        print('invalid input')
    else:
        if x == 1:
            print(a)
        else:
            print(a, end=' ')
            print(b, end=' ')
        for i in range(2, x):
            print(a+b, end=' ')
            c = a + b
            a = b
            b = c
fib(12)

Output: 0 1 1 2 3 5 8 13 21 34 55 89 

Fibonacci series with recursion:

def fib(x):
    if x <= 1:
        return x
    else:
        return fib(x - 1) + fib(x - 2)


terms = int(input("How many Fibonacci numbers to generate?"))
if terms <= 0:
    print("Invalid input. Please enter a positive integer.")
else:
    for i in range(terms):
        print(fib(i), end=' ')

Output:

How many Fibonacci numbers to generate? 12

0 1 1 2 3 5 8 13 21 34 55 89