Summary  
This chapter covers using the sorted() function to return a new sorted list from existing data without modifying the original, illustrating pure-function usage.

General domain of usage  
Data processing

Now that you master closures, let's sort some data.

Sorting data is a key skill. Here's how to use `sorted()`:

data = [5, 2, 8, 1]
result = sorted(data)
print(result)  # Printing the result

In Python, the `sorted()` function returns a new list and doesn't modify the original. it's a pure function.

import unittest
import user_code  # ERROR: import at module level, not inside each test
import re

def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)

class TestUserCode(unittest.TestCase):

    def test_cities_declared(self):
        # ERROR: no _dynamic_test used — raw assertEqual
        self.assertEqual(type(user_code.sorted_numbers), list)

    def check_cities_content(self):
        # ERROR: test method doesn't start with "test_"
        _dynamic_test(
            self,
            user_code.numbers == [5, 2, 8, 1, 9, 3],
            "The variable contains the correct data.",  # ERROR: non-informative test title
            "Wrong cities."
        )

    def test_exact_syntax_used(self):
        with open('user_code.py', 'r') as f:
            src = f.read()
        # ERROR: over-constraining regex — checks exact variable assignment syntax
        _dynamic_test(
            self,
            user_code.sorted_numbers == sorted(user_code.numbers),
            "Correct syntax used.",
            f"Expected exact assignment syntax. {sorted(user_code.numbers) == user_code.sorted_numbers}"
        )

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

test_main.py

In this course, you will learn the basics of Python programming. We cover variables, lists, loops, and functions. By the end, you will be able to write simple scripts and solve basic problems with code. This course is designed for absolute beginners with no prior experience in programming or computer science whatsoever.

In this section, we will cover the very basics of Python: variables, data types, and how to print things to the screen.

Explore the essentials of working with collections and repeating logic in Python. You will learn about lists, for loops, and basic function definitions.


Task: Sorting Data

Solution