fibonacci index lookup and prime tester with doctest

gistfile1.py

def fibonacci(n):
    """Return value at n in fibonacci sequence

    >>> fibonacci(3)
    3
    >>> fibonacci(6)
    13
    >>> fibonacci(9)
    55
    """
    x, y = 1, 1
    for i in xrange(n):
        x, y = y, x + y
    return x

def prime(n):
    """Return True if n is prime

    >>> prime(2)
    False
    >>> prime(7)
    True
    >>> prime(64)
    False
    """
    if not n % 2:
        return False
    for i in xrange(3, n, 2):
        if not n % i:
            return False
    return True

if __name__ == '__main__':
    import doctest
    doctest.testmod()