How to use a Python Dataclass in another class

Question

I'm trying to get to grips with Python and seem to be hitting a wall when trying to use Dataclasses. But when I run the test I have for it I get assertion error as it doesn't seem to see the dataclass right.

I have the following code:

file: music_library.py

from dataclasses import dataclass

@dataclass
class Track:
    title: str
    artist: str
    file: str

class MusicLibrary:
    def __init__(self):
        self.track = Track

    def all(self):
        return self.track

    def add(self, title, artist, file):
        self.track(title = title, artist = artist, file = file)

the add function is being called from a test and is passed the three arguments:

import unittest

from player.music_library import MusicLibrary


class TestMusicLibrary(unittest.TestCase):

    ml = MusicLibrary()

    def test_all(self):
        ml = MusicLibrary()
        ml.add("Track1", "artist1","file1")
        self.assertEqual(ml.all(), ["Track1","artist1","file1" ])

Yet the test fails with

Traceback (most recent call last):
  File "/projects/python/python-music-player-challenges/seed/tests/test_music_library.py", line 13, in test_all
    self.assertEqual(ml.all(), ["Track1","artist1","file1" ])
AssertionError: <class 'player.music_library.Track'> != ['Track1', 'artist1', 'file1']

What's going on here? I'm obviously missing something obvious.

Thanks

Answer 1

Update music_library.py like this:

from dataclasses import dataclass

@dataclass
class Track:
    title: str
    artist: str
    file: str


class MusicLibrary:
    def __init__(self):
        self.track = None

    def all(self):
        return self.track

    def add(self, title, artist, file):
        self.track = Track(title=title, artist=artist, file=file)

Pay attention to Dataclass instantiation in the above code.

And update your test case like this:

import unittest

from music_library import MusicLibrary


class TestMusicLibrary(unittest.TestCase):

    def test_all(self):
        ml = MusicLibrary()
        ml.add("Track1", "artist1", "file1")
        self.assertEqual([ml.all().title, ml.all().artist, ml.all().file],
                         ["Track1", "artist1", "file1"])

In your test code, you are comparing different object types, you should convert output of ml.all() to list first.

And if you run the test you get the following output:

Ran 1 test in 0.000s

OK