tail recurse exercise

recurse_ fib.py

"""
fun fib(n) =
    if n=1 then 1
    else if n=2 then 1
    else fib(n-1) + fib(n-2)
"""
def fib_loop(n):

    a = 1
    b = 2
    for i in xrange(1, n):
        a, b = a+b, a
    return a

def fib2(n):
    if n in [1,2]:
        return 1
    return fib2(n-1) + fib2(n-2)

def fib2_tail_recurse(n, res=1, t=1):
    if n==1:
        return res
    elif n==2:
        return res
    else:
        return fib2_tail_recurse(n-1, res+t, res)