Question

I want this function to return None if the lengths of a and b are the same, but it does not do that.

def longer(a: str, b: str):
return a if len(a) > len(b) else b

a. Modify the code so that None is returned in a certain case
b. Provide unit tests for this code
c. Give advice on why this might not be happening
d. Provide some sample output for this task​

Answer 1

To fix the function so it returns None when a and b are of the same length, add an explicit check. Unit tests ensure the function's correctness. The lack of the None check was a missing edge case, now corrected.

Step-by-step explanation:

To modify the function so that it returns None when the lengths of a and b are the same, you can add an explicit check for this condition. Here is the corrected version of the function:

a) def longer(a: str, b: str):
if len(a) == len(b):
return None
return a if len(a) > len(b) else b

b) To write unit tests for this function, you might use a testing framework like unittest in Python:

import unittest
class TestLongerFunction(unittest.TestCase):
def test_different_length(self):
self.assertEqual(longer('hello', 'hi'), 'hello')
def test_same_length_none(self):
self.assertIsNone(longer('no', 'go'))
def test_b_longer(self):
self.assertEqual(longer('short', 'longerstring'), 'longerstring')
unittest.main()

c) Reasons for the original function not returning None may include an oversight in handling the case where the strings are of equal length. This is an essential aspect of debugging and ensuring that all edge cases are covered in your code.

d) Here are some sample outputs:

• longer('hello', 'world') returns None
• longer('cat', 'mouse') returns 'mouse'
• longer('summer', 'fall') returns 'summer'

Answer 2

The function can be corrected to return None when strings are of equal length by adding an equality check. Unit tests should test different scenarios of string comparisons. Understanding the control flow is crucial for debugging such issues.

Step-by-step explanation:

To modify the function so that it returns None if the lengths of a and b are the same, we can add a check for equality in the condition. Here is the corrected code:

def longer(a: str, b: str):
if len(a) == len(b):
return None
return a if len(a) > len(b) else b

Unit tests for this function could be written in the following way:

import unittest
class TestLongerFunction(unittest.TestCase):
def test_same_length(self):
self.assertIsNone(longer('abc', 'def'))
def test_first_longer(self):
self.assertEqual(longer('long', 'sh'), 'long')
def test_second_longer(self):
self.assertEqual(longer('sh', 'long'), 'long')

if __name__ == '__main__':
unittest.main()

The reason the original function might not have been returning None could be due to the lack of an explicit check for equal string lengths. Remember that the else statement will execute if the lengths are the same, since the if condition only checks if a is longer than b and not if they are equal.

The corrected function would produce the following sample output:

• 
  
• longer('hello', 'world') returns None because both strings are the same length.
• 
  
• longer('python', 'java') returns 'python' because 'python' is longer than 'java'.
• 
  
• longer('go', 'swift') returns 'swift' because 'swift' is longer than 'go'.