Check input that belong to Fibonacci numbers in Python

Question

I would like to ask how can I retrieve out the list of fibo list and then check whether does the input value by the user is inside the fibo list.

    a , b = 1, 1
while num <= sys.maxint:
    fibo == a , b = b, a+b
    if num == (b +a+b):
        print "It is a Fibonacci number"        
        break
    else:
        print "It is not a Fibonacci number"
        break

Thank you!

Answer 1

Using a more sophisticated Fibonacci number test, you could use

def is_fibonacci(n):
    phi = 0.5 + 0.5 * math.sqrt(5.0)
    a = phi * n
    return n == 0 or abs(round(a) - a) < 1.0 / n

(This is probably the most efficient way to determine whether a number is a Fibonacci number, and it is most probably not the intended solution to your homework. I just included this answer for future reference.)

Answer 2

A pythonic one-liner

def is_fibonacci(n):
    return n >= 0 and (n==0 or sqrt( 5*n*n - 4).is_integer() or sqrt( 5*n*n + 4).is_integer())