Swift Navigation Problem

fibfeed.py

import math
import sys
import unittest


def fibfeed(N):
    """Computes the first N Fibonacci numbers F(n), where
        F(0) = 0
        F(1) = 1
        F(n) = F(n-1) + F(n-2)
    and prints the appropriate string for each one. N can take
    values from 0 to the maximum integer, and raises an
    exception otherwise.
    """
    if not isinstance(N, int):
        raise ValueError("N must be an integer.")
    if N < 0:
        raise ValueError("N must be at least 0.")
    # 0 is always printed.
    print 0
    # curr_f is the COUNT-th Fibonacci number
    count = 1
    prev_f, curr_f = 0, 1
    while count < N:
        print str_to_print(curr_f)
        prev_f, curr_f = curr_f, prev_f + curr_f
        count += 1
    print str_to_print(curr_f)


def str_to_print(f):
    """Returns the string that should be printed for an
    integer f, according to the assignment spec."""
    if not isinstance(f, int):
        raise ValueError("f must be an integer.")
    if f == 0:
        return str(f)
    elif f % 3 == 0:
        # when f % 15 == 0, this branch will always be reached
        if f % 5 == 0:
            return "FizzBuzz"
        # f can only be prime here if f == 3
        elif f == 3:
            return "BuzzFizz"
        return "Buzz"
    elif f % 5 == 0:
        # f can only be prime here if f == 5
        if f == 5:
            return "BuzzFizz"
        return "Fizz"
    elif is_prime(f):
        return "BuzzFizz"
    else:
        return str(f)


def is_prime(n):
    """Returns True if n is prime and False otherwise,
    with n an integer."""
    if not isinstance(n, int):
        raise ValueError("n must be an integer.")
    if n <= 1:
        return False
    for k in range(2, int(math.sqrt(n)) + 1):
        if n % k == 0:
            return False
    return True


class TestFibFeed(unittest.TestCase):

    def setUp(self):
        # expected outpupt up to F(20);
        # F(20) is the first divisible by 15
        self.expected20 = [
            "0",
            "1",
            "1",
            "BuzzFizz",
            "BuzzFizz",
            "BuzzFizz",
            "8",
            "BuzzFizz",
            "Buzz",
            "34",
            "Fizz",
            "BuzzFizz",
            "Buzz",
            "BuzzFizz",
            "377",
            "Fizz",
            "Buzz",
            "BuzzFizz",
            "2584",
            "4181",
            "FizzBuzz"
        ]

    def test_is_prime(self):
        with self.assertRaises(ValueError):
            is_prime("hello")
            is_prime(True)
            is_prime(2.7)
        self.assertFalse(is_prime(0))
        self.assertFalse(is_prime(1))
        self.assertTrue(is_prime(2))
        self.assertTrue(is_prime(3))
        self.assertFalse(is_prime(4))
        self.assertTrue(is_prime(5))
        self.assertFalse(is_prime(6))
        self.assertTrue(is_prime(7))
        self.assertFalse(is_prime(8))
        self.assertFalse(is_prime(9))
        self.assertFalse(is_prime(10))
        self.assertTrue(is_prime(11))
        self.assertFalse(is_prime(12))
        self.assertTrue(is_prime(13))
        self.assertFalse(is_prime(14))
        self.assertFalse(is_prime(15))

    def test_str_bad_input(self):
        with self.assertRaises(ValueError):
            str_to_print("hello")
            str_to_print(True)
            str_to_print(2.7)

    def test_str_3(self):
        for k in range(2, 100 / 3):
            if k % 5 != 0:
                self.assertEqual(str_to_print(k * 3), "Buzz")

    def test_str_5(self):
        for k in range(2, 100 / 5):
            if k % 3 != 0:
                self.assertEqual(str_to_print(k * 5), "Fizz")

    def test_str_15(self):
        for k in range(1, 100 / 15):
            self.assertEqual(str_to_print(k * 15), "FizzBuzz")

    def test_str_prime(self):
        self.assertEqual(str_to_print(2), "BuzzFizz")
        self.assertEqual(str_to_print(3), "BuzzFizz")
        self.assertEqual(str_to_print(5), "BuzzFizz")
        self.assertEqual(str_to_print(7), "BuzzFizz")
        self.assertEqual(str_to_print(11), "BuzzFizz")
        self.assertEqual(str_to_print(13), "BuzzFizz")
        self.assertEqual(str_to_print(43), "BuzzFizz")
        self.assertEqual(str_to_print(97), "BuzzFizz")

    def test_str_no_fit(self):
        self.assertEqual(str_to_print(0), "0")
        self.assertEqual(str_to_print(1), "1")
        self.assertEqual(str_to_print(4), "4")
        self.assertEqual(str_to_print(8), "8")
        self.assertEqual(str_to_print(14), "14")

    def test_fibfeed_3(self):
        expected = '\n'.join(self.expected20[:4])
        fibfeed(3)
        output = sys.stdout.getvalue().strip()
        self.assertEquals(output, expected)

    def test_fibfeed_20(self):
        expected = '\n'.join(self.expected20)
        fibfeed(20)
        output = sys.stdout.getvalue().strip()
        self.assertEquals(output, expected)

if __name__ == "__main__":
    unittest.main(module=__name__, buffer=True, exit=False)