Function to get the nth Fibonacci term in linear time and constant space.

get_n_th_fibo.py

def get_n_th_fibo(n):
    '''
    Returns the nth term of the fibonacci sequence - {0, 1, 1, 2, ...}
    
    F(n) = F(n-1) + F(n-2) where n>=2
    F(0) = 0
    F(1) = 1
    '''
    if n == 0:
        return 0
    elif n in [1, 2]:
        return 1
    a, b = 1, 1
    while n>2:
        a, b = b, a+b
        n -= 1
    return b