Python Dynamic Programming

def fb(n):
    if n ==1: return 1

    n1, n2 = 0, 1 #f(1)=0, f(2)=1
    sum = 0
    for i in range(n-2): #f(n=3) = f(1) + f(2), once = range(1)  
        n1, n2 = n2, n1+n2
        sum = n1 + n2
    return sum

if __name__== "__main__":
    print fb(10)

    '''#testing range
    for i in range(1):
        print i #print once, i = 0
    '''