This notebook was prepared by Donne Martin. Source and license info is on GitHub.

# Challenge Notebook¶

## Constraints¶

• Can we assume the inputs are valid?
• No, check for None
• Can we assume this fits memory?
• Yes

## Test Cases¶

* None input -> TypeError
* 7, 5 -> 2
* -5, -7 -> 2
* -5, 7 -> -12
* 5, -7 -> 12


## Algorithm¶

Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

## Code¶

In [ ]:
class Solution(object):

def sub_two(self, val):
# TODO: Implement me
pass


## Unit Test¶

The following unit test is expected to fail until you solve the challenge.

In [ ]:
# %load test_sub_two.py
import unittest

class TestSubTwo(unittest.TestCase):

def test_sub_two(self):
solution = Solution()
self.assertRaises(TypeError, solution.sub_two, None)
self.assertEqual(solution.sub_two(7, 5), 2)
self.assertEqual(solution.sub_two(-5, -7), 2)
self.assertEqual(solution.sub_two(-5, 7), -12)
self.assertEqual(solution.sub_two(5, -7), 12)
print('Success: test_sub_two')

def main():
test = TestSubTwo()
test.test_sub_two()

if __name__ == '__main__':
main()


## Solution Notebook¶

Review the Solution Notebook for a discussion on algorithms and code solutions.