MCS-177 Project 9: Music Library (Fall 2015)

Start: Tuesday 12/1; Due: Wednesday 12/9, by the beginning of class

Overview

In this project, you will experiment with building your own Python classes. Many of you have music files on your computer and organize them into playlists. You will build classes to represent your music files and playlists to organize them.

You may do this project with a partner. If you choose to work with a partner, please only submit one copy of the code with both names written in each of the Python files as a comment.

Specific tasks

1. Implement the Song class in song.py such that:
   • Each Song object contains the artist, album title, song title, mp3 file name, and genre.
   • The Song class provides accessor and mutator methods for all instance variables.
   • Blank strings (those containing only white space) are not valid for any instance variables. Mutator methods must print an error messsage and not modify the corresponding instance variable if a blank string is provided.

   • When a Song object is printed, it shows the artist, album title, and song title. For example, if you print the song "Just Dance" in The Fame by Lady Gaga, you should see:

     Just Dance in The Fame by Lady Gaga

2. Implement the Playlist class in playlist.py such that:
   • Each playlist contains a name, a list of Song objects, and an indication whether the playlist is to be played in a random order.
   • The Playlist class provides accessor and mutator methods for the instance variables you use for the name, list of songs, and random-play indication.
   • A blank string is not valid for the instance variable you use for the name. The corresponding mutator method must print an error messsage and not modify the instance variable if a blank string is provided.

   • When a Playlist object is printed, it shows the playlist name and all the songs in the playlist. For example, if you print the playlist whose name is "Lady Gaga Mix" and which contains two songs: "Just Dance" in The Fame by Lady Gaga and "Americano" in Born This Way by Lady Gaga, you should see:

     Playlist: Lady Gaga Mix
Just Dance in The Fame by Lady Gaga
Americano in Born This Way by Lady Gaga


   • The Playlist class provides a method called nextSong which returns the next Song object to play in the playlist. If the playlist is played in the original order, it should return the next song in the list. If the playlist is played in a random order, it should return a song that has not been played yet. It should only repeat a song if all songs in the playlist have been played. This ensures that the playlist does not keep returning same two songs over and over again.

     Notes and considerations

     • The list of songs is re-permuted after every song is played once. This means that the same song can potentially played twice in a row if the song is played as the last song in one permutation and it is picked as the first song in the next permutation. Also, you could in principle keep getting the same permutation repeatedly, but if you see this happening, you ought to suspect that you aren't re-permuting the list when you ought to be.
     • Think about what would happen if a user uses the mutator method to toggle the play order. If the play order is changed from random to non-random, then the nextSong method should return the first song in the original list of songs. If the play order is changed from non-random to random, it should start returning songs in a random order as described above.
     • Also think about what would happen if a user uses the mutator method to change the list of songs. If the play order is non-random, the nextSong method should return the first song in the new list of songs. If the player order is random, it should return a random song in the new list of songs.

     Example of a playlist of 3 songs (A, B, C)

     Non-random order	Random Order
     	Correct	Incorrect	Suspicious
     Song A Song B Song C Song A Song B Song C Song A Song B Song C . . .	Song C Song B Song A Song B Song A Song C Song C Song A Song B . . . (Notice how each song appears only once in songs 1-3, 4-6, etc.)	Song C Song B Song C Song A Song B Song A Song B Song C Song A . . . (Notice how Song C reappears before all 3 songs are played.)	Song B Song C Song A Song B Song C Song A Song B Song C Song A . . . (Notice how the same permutation (B, C, A) keeps repeating.)

3. Make at least two sample playlists, each with at least 3 songs, by placing appropriate assignment statements in sample.py. (Make sure there are at least 5 unique songs in your examples.)

Having fun with your songs and playlists

NOTE: This only works on Macs (Mac OS X).

1. Place all your Python files (song.py, playlist.py, and sample.py) and your MP3 files that you used in the samples in the same directory.
2. Download play.py into the same directory.
3. Open Terminal by typing "Terminal" (without quotation marks) in Spotlight (the magnifying class at the top right corner of the screen).
4. Navigate to the directory where you have all your files using the command cd.
5. Type python to enter the Python shell.
6. Type from play import * into the Python shell.
7. Type play(myPlaylist1) into the Python shell (or any other playlists you created in sample.py), and enjoy your music!
8. You can press ctrl-c (CTRL key and C key at the same time) to stop playing the playlist.

Submitting your work

You will be submitting your code using Moodle; click on the following link for instructions on submitting code using Moodle. For this project, you will need to submit the following files:

• song.py, which contains all implementation and documentation for the Song class.
• playlist.py, which contains all implementation and documentation for the Playlist class.
• sample.py, which contains all your test songs and playlists.

Grading

You will earn one point for each of the following accomplishments:

1. You have all the instance variables necessary for the Song class.
2. You have accessor methods for all the specified instance variables in the Song class.
3. You have mutator methods for all the specified instance variables in the Song class.
4. The mutator methods in the Songclass respond to a blank string by printing an error message and not changing the instance variable.
5. The Song class provides a special method such that you can convert a Song object into a string, which would aautomatically be used for printing.
6. You have all the instance variables necessary for the Playlist class.
7. You have accessor methods for all the specified instance variables in the Playlist class.
8. You have mutator methods for all the specified instance variables in the Playlist class.
9. The name mutator method in the Playlistclass responds to a blank string by printing an error message and not changing the instance variable.
10. The Playlist class provides a special method such that you can convert a Playlist object into a string, which would be automatically used for printing.
11. The nextSong method returns a Songobject.
12. The nextSong method returns the correct Song object when the Playlist is set to non-random order.
13. The nextSong method returns the correct Song object when the Playlist is set to random order.
14. The nextSong method does not return the same Song object until all Song objects have been returned by the nextSong.
15. You wrote the correct contract for each accessor method in the Song and Playlist classes.
16. You wrote the correct contract for each mutator method in the Song and Playlist classes.
17. You wrote the correct contract for the nextSong method in the Playlist class.
18. Your code is not unneccessarily complex.
19. You construct at least 5 Song objects in sample.py.
20. You construct at least 2 Playlist objects with different names and songs in sample.py.