By nine

main.py

@@ -5,16 +5,22 @@ def divide_by_two(num): # Take last digit, divide by two only on that
     return _get_last_digit(num) % 2 == 0
 
 def divide_by_three(num): # Sum each digit in number, then check divisibility of that number
-    num_string = f"{num}"
-    num_sum = 0
-    for digit_char in num_string:
-        num_sum += int(digit_char)
-    return num_sum % 3 == 0
+    return _sum_digits(num) % 3 == 0
 
 def divide_by_five(num): # If last digit is a zero or a five return true
     last_digit = _get_last_digit(num)
     return last_digit == 0 or last_digit == 5
 
+def divide_by_nine(num): # Sum each digit in number, then check divisibility of that number
+    return _sum_digits(num) % 9 == 0
+
 def _get_last_digit(num):
     return int(f"{num}"[-1])
 
+def _sum_digits(num):
+    num_string = f"{num}"
+    num_sum = 0
+    for digit_char in num_string:
+        num_sum += int(digit_char)
+    return num_sum
+

tests/nine_test.py

@@ -0,0 +1,16 @@
+from main import divide_by_nine
+import unittest
+
+class TestDivideByNine(unittest.TestCase):
+    def test_by_1(self):
+        self.assertFalse(divide_by_nine(1))
+    def test_by_3(self):
+        self.assertFalse(divide_by_nine(3))
+    def test_by_9(self):
+        self.assertTrue(divide_by_nine(9))
+    def test_by_10(self):
+        self.assertFalse(divide_by_nine(10))
+    def test_by_18(self):
+        self.assertTrue(divide_by_nine(18))
+    def test_by_362880(self):
+        self.assertTrue(divide_by_nine(362880))