Fixed audio_features API wrapper function return structure (#653)

Co-authored-by: Stéphane Bruckert <stephane.bruckert@gmail.com>

CHANGELOG.md

@@ -5,14 +5,18 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+
 ## Unreleased [3.0.0-alpha]
 
 While this is unreleased, please only add v3 features here.
 Rebasing master onto v3 doesn't require a changelog update.
 
-### Added
-
-- ...
+### Changed
+Modified the return structure of the `audio_features` function (wrapping the [Get Audio Features for Several Tracks](https://developer.spotify.com/documentation/web-api/reference/#endpoint-get-several-audio-features) API) to conform to the return structure of similar APIs, such as:
+ - [Get Several Tracks](https://developer.spotify.com/documentation/web-api/reference/#endpoint-get-several-tracks)
+ - [Get Multiple Artists](https://developer.spotify.com/documentation/web-api/reference/#endpoint-get-multiple-artists)
+ - [Get Multiple Albums](https://developer.spotify.com/documentation/web-api/reference/#endpoint-get-multiple-albums)
+The functions wrapping these APIs do not unwrap the single key JSON response, and this is currently the only function that does this.
 
 ## Unreleased [2.x.x]
 

spotipy/client.py

@@ -1623,12 +1623,7 @@ class Spotify(object):
         else:
             tlist = [self._get_id("track", t) for t in tracks]
             results = self._get("audio-features/?ids=" + ",".join(tlist))
-        # the response has changed, look for the new style first, and if
-        # its not there, fallback on the old style
-        if "audio_features" in results:
-            return results["audio_features"]
-        else:
-            return results
+        return results
 
     def devices(self):
         """ Get a list of user's available devices.

tests/integration/test_non_user_endpoints.py

@@ -67,19 +67,19 @@ class AuthTestSpotipy(unittest.TestCase):
 
     def test_audio_features(self):
         results = self.spotify.audio_features(self.four_tracks)
-        self.assertTrue(len(results) == len(self.four_tracks))
-        for track in results:
+        self.assertTrue(len(results['audio_features']) == len(self.four_tracks))
+        for track in results['audio_features']:
             assert('speechiness' in track)
 
     def test_audio_features_with_bad_track(self):
         bad_tracks = ['spotify:track:bad']
         input = self.four_tracks + bad_tracks
         results = self.spotify.audio_features(input)
-        self.assertTrue(len(results) == len(input))
-        for track in results[:-1]:
+        self.assertTrue(len(results['audio_features']) == len(input))
+        for track in results['audio_features'][:-1]:
             if track is not None:
                 assert('speechiness' in track)
-        self.assertTrue(results[-1] is None)
+        self.assertTrue(results['audio_features'][-1] is None)
 
     def test_recommendations(self):
         results = self.spotify.recommendations(