Summary  
This chapter explains how to use a while loop to repeatedly execute a block of code based on a Boolean condition and how to manage an index variable to safely traverse elements without exceeding bounds.

General domain of usage  
Iterating through list elements

The `while` loop is used to repeat a block of code as long as a specified condition evaluates to `True`. The condition is checked at the beginning of each iteration, and the loop stops when the condition becomes `False`.
``` python
while condition:
    # Code to execute while the condition is True
```
`condition`: a Boolean expression that evaluates to `True` or `False`.

We will print all destinations from the `travel_list` one by one.

travel_list = ['Monako', 'Luxemburg', 'Liverpool', 'Barcelona', 'Munchen']

# Initialize the index
i = 0

# Print each destination using a while loop
while i < len(travel_list):
    print(travel_list[i])
    i += 1

- The variable `i` starts at `0`, which represents the first index of the `travel_list`;
- The while loop checks if `i` is less than the length of the list (`len(travel_list)`). This ensures the loop doesn't exceed the list bounds;
- The loop prints the destination at the current index `travel_list[i]`;
- The variable `i` is incremented by `1` in each iteration using `i += 1`;
- When `i` becomes equal to the length of the list, the condition evaluates to `False`, and the loop stops.

import unittest
import importlib
import re

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

class TestUserCode(unittest.TestCase):

    def test_selected_is_declared(self):
        try:
            user_code = importlib.import_module("user_code")
            _dynamic_test(
                self,
                hasattr(user_code, 'selected'),
                "The `selected` list is declared.",
                "Expected `selected` to be declared."
            )
        except ImportError as e:
            self.fail(f"Failed to import module: {e}")

    def test_selected_contains_correct_values(self):
        try:
            user_code = importlib.import_module("user_code")
            expected_selected = user_code.countries[:len(user_code.countries) // 2]
            _dynamic_test(
                self,
                user_code.selected == expected_selected,
                "The `selected` list contains the first half of the countries.",
                f"Expected `selected` to be `{expected_selected}`, but got `{user_code.selected}`."
            )
        except AttributeError as e:
            _dynamic_test(self, False, "", f"Missing variable: {e}")
        except ImportError as e:
            self.fail(f"Failed to import module: {e}")

    def test_while_loop_is_used(self):
        try:
            with open("user_code.py", "r") as file:
                source_code = file.read()
            _dynamic_test(
                self,
                re.search(r"while", source_code) is not None,
                "A while loop is used to select the first half of the countries.",
                "Expected a while loop to be used in the script."
            )
        except FileNotFoundError:
            self.fail("Failed to open `user_code.py`. Make sure the file exists.")

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

test_main.py

Build confidence in mastering Python loops! Start with the basics of for and while loops and progress to advanced concepts like nested loops, control statements, and dynamic conditions. With hands-on practice and real-world examples, gain the skills to write efficient, clean, and powerful code. Perfect for beginners and anyone looking to sharpen their Python expertise!

Master how to iterate through sequences with for loop, use range() effectively, explore conditions with if/else, and control loops with break and continue. Get ready to write efficient, clean, and practical code as you tackle fun challenges!

Get hands-on experience with the while loop! Learn how to handle conditions, avoid infinite loops, control flow with break and continue, and even combine else with your loops. Master when to use while loops effectively in real-world scenarios and sharpen your problem-solving skills!

Learn how to combine loops effectively, use if/else conditions, and master break and continue statements to control flow. By the end, you'll be able to solve complex problems with ease and precision.

Streamline your Python code with list and dictionary comprehensions! Learn how to create lists and dictionaries in a concise and elegant way while improving readability and performance. Master practical examples and discover how to simplify complex tasks, from filtering data to transforming it, all in a single line of code.

The First while Loop

Solution