Media player refactoring kata in Python

Overview

This kata complements Clean Code: SOLID, Ep. 12 - Interface Segregation Principle.

The exercise involves refactoring a multimedia player system to adhere to this principle.

The problem involves different types of media: audio, video, and images. We start with a monolithic IMediaPlayer interface that handles all types of media. This will be your starting point.

Instructions

Exercise 1

In the first part, your task is to refactor the existing code such that each type of media player (audio, video, and image) has its own specific interface, instead of the monolithic IMediaPlayer interface. You should create IAudioPlayer, IVideoPlayer, and IImagePlayer interfaces, each with a relevant method, and update the AudioPlayer, VideoPlayer, and ImagePlayer classes to implement these new interfaces.

This part includes unit tests that ensure each type of media player is functioning correctly. After you have completed your refactoring, all unit tests should pass.

Exercise 2

In the second part, we will deal with the compatibility of different players with different file types.

Before, we had a separate player for each media type. We want to have media files that come in different formats (e.g., .mp3, .flac, .wav for audio, .jpeg, .png for images, and .mp4, .mkv for videos), and some players can only handle certain formats.

We have the MediaFile class to represent a media file. Your task is to:

1. Update the player interfaces to take MediaFile objects, e.g.:

   class IAudioPlayer(ABC):
   
       @abstractmethod
       def play_audio(self, file):
           pass

2. Create specialized players that can only handle certain formats (i.e., Mp3Player, FlacPlayer, WavPlayer).

   class Mp3Player(IAudioPlayer):
   
       def play_audio(self, file):
           if file.format != "mp3":
               raise ValueError("Invalid file format for Mp3Player!")
   
           # Implementation...

   The same kind of specialization will be done for FlacPlayer, WavPlayer, and respective video and image players.

3. Add corresponding unit tests, e.g.:

   def test_mp3_player_handles_mp3():
       mp3_player = Mp3Player()
       mp3_file = MediaFile(format="mp3", filename="")
       mp3_player.play_audio(mp3_file)
   
   def test_mp3_player_rejects_non_mp3():
       mp3_player = Mp3Player()
       flac_file = MediaFile(format="flac", filename="")
       with pytest.raises(ValueError):
           mp3_player.play_audio(flac_file)

Exercise 3

In the third part, we introduce the concept of a MediaListPlayer. This class accepts a list of media files and a corresponding list of players. It checks whether the player is compatible with the media file format before trying to play/display the file.

For the MediaListPlayer, we can update the play_list method to take a list of IAudioPlayer, IVideoPlayer, and IImagePlayer instead of IMediaPlayer.

In the play_list method, we should use the appropriate player based on the type of the media file. This may require additional checks or mappings from file type to player.

Your task is to refactor the code to segregate interfaces based on the different file formats and adapt the MediaListPlayer to work with the new classes and interfaces.

Refactor the Python implementation without changing its existing behavior. Setup is complete when all three existing tests pass.

Prerequisites

Required:

• Git
• uv

Optional:

• GNU Make, for shorter commands. Every required task also has a direct uv command.

You do not need to install Python or pytest separately. uv installs a compatible Python version and the locked project dependencies when needed.

Set up the kata

1. Clone the repository:

   git clone https://github.com/Coding-Cuddles/media-player-refactoring-python-kata.git

2. Enter the repository directory:

   cd media-player-refactoring-python-kata

3. Run the existing tests. Use Make when it is installed:

   make test

   Otherwise, run pytest through uv directly:

   uv run pytest test_*.py

   The first run may install Python and the project dependencies. Setup is complete when pytest reports 3 passed.

   If the command fails with uv: command not found, install uv and repeat this step.

Work on the kata

1. Start Exercise 1 in media_player.py. Update test_media_player.py as you add behavior.

2. Run the tests after each change. Use Make when it is installed:

   make test

   Otherwise, run pytest through uv directly:

   uv run pytest test_*.py

   Continue when the test run passes.

Make command reference

Make is optional. Run make or make help to list these commands in the terminal.

Command	Result
make all	Run the test suite
make help	Show the command reference
make test	Run the test suite
make format	Format tracked Python files
make format-check	Check formatting without changing files
make clean	Remove generated caches