Learn Python Loops and lists Interactively

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This tutorial contains 45 auto-graded Python exercises about lists, loops, dictionaries and matrices, plus a welcome page, all inside one LearnPack package. Every exercise folder ships an app.py, a test.py and a reference solution.hide.py, and the whole package is graded by 131 individual pytest checks. Estimated duration: 10 hours, difficulty easy, Python 3. Instructions are available in English and Spanish, and 13 exercises include a video walkthrough.

📋 About this tutorial

• Difficulty: easy (beginner, no previous loop experience needed)
• Estimated duration: 10 hours
• Technologies: Python 3, pytest, LearnPack
• Exercises: 45 auto-graded exercises + 1 welcome page
• Automatic grading: yes — 131 pytest checks across 45 test.py files
• Video solutions: 13 exercises embed a YouTube walkthrough
• Languages: instructions in English and Spanish (README.md and README.es.md inside every exercise)

🎯 What will you learn?

• Access and mutate lists by index, where the first position is 0: read the 3rd item with my_list[2], replace a value, and print a specific position.
• All the ways of looping in Python: for item in my_list, for i in range(start, stop, step) and while, including a countdown from 20 to 1 that ends with LIFTOFF.
• Accumulator patterns written by hand: totals, averages, maximums and minimums built with a for loop and an auxiliary variable instead of sum() or max().
• Transform lists with map() across 7 exercises: converting Celsius to Fahrenheit, mapping a list with an already-defined function, printing the data type of every item with type(), and mapping a list of dictionaries.
• Remove elements with filter() across 5 exercises: numbers greater than 10, names that start with a given letter, completed tasks inside a list of dictionaries, and a final one that combines filter() with map() to build <li> HTML tags.
• Work with dictionaries: read and add keys, loop over keys and values, and count letter frequencies ignoring case and spaces.
• Build and read 2-dimensional lists (matrices): generate an N×N matrix of 1s and analyse a parking-lot grid with a nested loop.

👀 What will you build?

The 45 exercises are small, self-contained programs that grow in difficulty. Some of the ones you will solve:

• 03 Flip list — turn [45, 67, 87, 23, 5, 32, 60] into [60, 32, 5, 23, 87, 67, 45] by looping the list and appending each item into a new one.
• 07 Do While — print every number from 20 down to 1 with a while loop, adding an exclamation mark to multiples of 5, and finish with LIFTOFF.
• 08.2 Divide and conquer — a sort_odd_even() function that returns one single flat list with the odd numbers first and the even ones after.
• 09 Max integer — a max_integer() function that receives a list and returns the biggest number using a for loop and an if.
• 12 Map a list — convert a list of Celsius temperatures into [28.4, 93.2, 132.8, 14.0] inside a map() call.
• 13.4 Making HTML with filter and map — combine both functions to output ['<li>Red</li>', '<li>Orange</li>', '<li>Pink</li>', '<li>Violet</li>'].
• 14.1 Letter counter — count how many times each letter appears in a text and print a dictionary such as {'h': 1, 'e': 1, 'l': 3, 'o': 2, ...}.
• 15.2 Parking lot — a get_parking_lot() function that receives a matrix and returns total_slots, available_slots and occupied_slots.
• 16 Techno Beats — the final challenge: a lyrics_generator() function that turns [0, 0, 1, 1, 1, 0] into Boom and Drop the bass beats, adding !!!Break the bass!!! every time it finds three 1s in a row.

🎓 What do you need before starting?

• Python basics: variables, print(), if/else and how to declare a function. If you have never written Python, start with Learn Python Interactively (beginner) first.
• No installation if you open the tutorial in GitHub Codespaces or Gitpod: the container already installs Python 3.10, LearnPack and pytest for you (the Codespaces dev container also adds Node.js 22).
• For a local setup: Python 3, Node.js 14+ and npm, so you can install LearnPack and run learnpack start.
• Zero previous knowledge of loops: exercise 01 is a plain print("Hello World") and the difficulty ramps up from there.

✅ How does the automatic grading work?

Each of the 45 exercises has a test.py file executed with pytest (version 6.2.5, with pytest-testdox for readable output). Together they contain 131 named checks, and they grade your work in three different ways:

• Console output: 40 exercises capture what your program prints and compare it against the expected text, character by character, including line breaks.
• Function behaviour: 9 exercises require a function with an exact name, and 4 of them (09, 12.6, 15.1 and 15.2) call that function with their own inputs and compare the returned value, so printing instead of returning is not enough.
• Source code inspection: 39 exercises open your app.py and scan its text (some with a regular expression, some with a plain search) to make sure you actually used the construct being taught — for, while, if, print, map, filter, type or import random, depending on the exercise.

Every exercise folder also contains solution.hide.py with a reference solution, so you can compare approaches once you have solved it yourself.

💡 The tests are deliberately strict about output formatting. If your logic is right but a test still fails, compare your output with the "Expected result" block in the exercise instructions, space by space.

💡 What mistakes should you avoid?

• Printing when the test expects a return. In 16 Techno Beats the last lines of app.py already call print(lyrics_generator([0,0,1,1,0,0,0])), so your function must return the string. If you print inside the function, the output is duplicated and the test fails.
• Ignoring the function parameter. The 15.2 Parking lot test calls get_parking_lot() with its own matrices, not with the global parking_state variable. A function that reads the global list instead of its argument fails the second and third checks.
• Miscounting the parking-lot values. In 15.2 a 0 is not a parking slot: only 1 (occupied) and 2 (available) count towards total_slots. For [[1,1,1], [0,0,0], [1,1,2]] the expected answer is {'total_slots': 6, 'available_slots': 1, 'occupied_slots': 5}.
• Replacing map() or filter() with a list comprehension. The 12.x tests literally search for the text map inside your app.py, and the 13.x tests search for filter, so a comprehension that prints the right result is not enough. The same happens with sum() in 05 or max() in 09: those tests require a for loop in your code.
• Leaving debugging print() calls behind. In 05 Sum all items and 13.4 the test compares the entire console output with the expected string, so any extra line breaks the assertion.
• Printing the map() or filter() object instead of the list. Wrap the result in list(); the expected output looks like [23, 12, 35, 54, 21, 534, 23, 42], not <filter object at 0x...>.
• Off-by-one indexes. Lists start at 0, so the "3rd item" is my_list[2] and thursday in a week list lives at my_list[4]. Exercise 01.1 imports my_list from your file and asserts that position 4 is None, so do not rename or delete the variables that come predefined in app.py.

❓ Frequently asked questions

Do I need to install anything to start?

No. Opening the repository in GitHub Codespaces or Gitpod builds a container with Python 3.10, LearnPack and pytest already installed, and the exercises start on their own. Installing locally is optional and takes two commands.

Do I need to know Python before starting these exercises?

You need the very basics: variables, print(), if/else and function declarations. Lists, indexes, loops, map(), filter(), dictionaries and matrices are all explained from scratch inside the exercise instructions.

How long does it take to complete the 45 exercises?

The package is estimated at 10 hours of work. The first exercises take a couple of minutes each, while the final ones (15.2 Parking lot and 16 Techno Beats) require nested loops and auxiliary counters and can take considerably longer.

Can I solve the exercises with list comprehensions instead of map() and filter()?

Not if you want the tests to pass. The seven map() exercises and the five filter() exercises inspect your source code and look for the corresponding function inside app.py. Once you have passed them, rewriting the solution as a comprehension is an excellent extra practice.

Why does my exercise fail if the console output looks correct?

Because the assertions compare exact strings. A missing trailing space, a different number of decimals, single quotes instead of double quotes inside a printed list, or an extra debugging line are enough to fail. Copy the "Expected result" block from the instructions and compare it literally with your output.

Is this tutorial free, and can I reuse the code?

Access to the exercises costs nothing and the solutions you write are yours to keep and reuse. The tutorial content itself is not open source: the LICENSE reserves all intellectual property rights and does not allow republishing, selling or redistributing the material.

📚 Related tutorials

• Learn Python Interactively (beginner) — the recommended step before this one.
• Learn Python Functions Interactively — parameters, return values and scope.
• Learn Object Oriented Programming with Python — classes and objects.
• Master Python by practice (interactive) — a bigger challenge once loops feel natural.

🚀 How to start

The fastest way is to open the repository in a ready-made cloud environment:

1. Click Open in Codespaces (recommended) or Open in Gitpod.

2. Wait for the container to finish building. It installs Python 3.10, pytest, LearnPack and the LearnPack Python plugin (in Codespaces it also installs Node.js 22).

3. The LearnPack exercises should open automatically. If they do not, run this in the terminal:

   $ learnpack start

There is also an intro video for the whole tutorial: Python lists and loops introduction.

💻 Local installation

1. Install LearnPack and its Python plugin (you need Node.js 14+ and Python 3):

   $ npm i @learnpack/learnpack@5.0.348 -g && learnpack plugins:install @learnpack/python@1.0.6

2. Clone this repository and enter the folder:

   $ git clone https://github.com/4GeeksAcademy/python-lists-loops-programming-exercises.git
   $ cd python-lists-loops-programming-exercises

3. Install the testing dependencies and start the tutorial from the same folder that contains learn.json:

   $ pip3 install pytest==6.2.5 pytest-testdox mock
   $ learnpack start

📝 How the exercises are organized

Every exercise lives in its own folder inside exercises/ and contains the same set of files:

1. app.py — the file you edit; it is the Python script that gets executed.

2. README.md and README.es.md — the instructions in English and Spanish, sometimes with a linked video tutorial.

3. test.py — the grading script. You do not need to open it, but reading it tells you exactly what is being checked.

4. solution.hide.py — the reference solution for that exercise.

Found a bug or a typo? Report it here; these exercises are built collaboratively and every report helps.

🤝 Contributors

Thanks to these wonderful people (emoji key):

1. Alejandro Sánchez (alesanchezr) — (coder) 💻, (idea) 🤔, (build-tests) ⚠️, (pull-request-review) 👀, (build-tutorial) ✅, (documentation) 📖

2. Paolo (plucodev) — (bug reports) 🐛, (coder) 💻, (translation) 🌎

See the full list of contributors. This project follows the all-contributors specification; contributions of any kind are welcome.

This and many other exercises are built by students as part of the 4Geeks Academy coding bootcamp. Learn more about the Full Stack Developer career program and the Data Science and Machine Learning career program.