What methods can be used to verify the correct functioning of written code?

To ensure the correct functioning of Python code, you can use the following methods:

• Unit testing: writing tests for individual functions or classes using modules like unittest, pytest, or doctest.
• Debugging: running the code in debug mode with a built-in debugger (pdb) or an IDE for step-by-step analysis.
• Logging: adding logs to track the program's state and identify errors.
• Manual testing: checking the code's operation with different input data.
• Static code analysis: using tools like flake8, pylint to identify potential errors and style violations.

Example of a simple unit test using unittest:

import unittest

def add(a, b):
    return a + b

class TestAddFunction(unittest.TestCase):
    def test_add_positive(self):
        self.assertEqual(add(2, 3), 5)

    def test_add_negative(self):
        self.assertEqual(add(-1, -1), -2)

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