fixes: #159 Refactored grab_playlist (#160)

* Refactored grab_playlist

grab_playlist was looping through the user's playlist until it finds the playlist.
In some cases a public playlist isn't in the user's playlists
Using a more direct approach, querying for the tracks of a playlist

* Remove old `def write_playlist()`

* Playlist URL download now works on private playlists

spotdl.py

@@ -217,16 +217,16 @@ def write_tracks(text_file, tracks):
                 break
 
 
-def write_playlist(playlist):
+def write_playlist(username, playlist_id):
     results = spotify.user_playlist(
-        playlist['owner']['id'], playlist['id'], fields='tracks,next')
-    text_file = u'{0}.txt'.format(slugify(playlist['name'], ok='-_()[]{}'))
-    print(u'Feeding {0} tracks to {1}'.format(playlist['tracks']['total'], text_file))
+            username, playlist_id, fields='tracks,next,name')
+    text_file = u'{0}.txt'.format(slugify(results['name'], ok='-_()[]{}'))
 
+    print(u'Feeding {0} tracks to {1}'.format(results['tracks']['total'], text_file)) 
     tracks = results['tracks']
     write_tracks(text_file, tracks)
 
-
+    
 def write_album(album):
     tracks = spotify.album_tracks(album['id'])
     text_file = u'{0}.txt'.format(slugify(album['name'], ok='-_()[]{}'))
@@ -340,24 +340,9 @@ def grab_playlist(playlist):
 
     username = splits[-3]
     playlist_id = splits[-1]
-    playlists = spotify.user_playlists(username)
-    found = False
-
-    while True:
-        for playlist in playlists['items']:
-            if not playlist['name'] == None:
-                if playlist['id'] == playlist_id:
-                    playlists['next'] = None
-                    found = True
-                    break
-        if playlists['next']:
-            playlists = spotify.next(playlists)
-        else:
-            break
-
-    if found:
-        write_playlist(playlist)
-    else:
+    try:
+        write_playlist(username, playlist_id)
+    except spotipy.client.SpotifyException:
         print('Unable to find playlist')
         print('Make sure the playlist is set to publicly visible and then try again')