diff --git a/mopidy/backends/__init__.py b/mopidy/backends/__init__.py
index e45dcf63..1a7e1559 100644
--- a/mopidy/backends/__init__.py
+++ b/mopidy/backends/__init__.py
@@ -104,7 +104,7 @@ class BaseCurrentPlaylistController(object):
         tracks = self.playlist.tracks
 
         assert at_position <= len(tracks), 'at_position can not be greater' \
-            + ' than  playlist length'
+            + ' than playlist length'
 
         if at_position is not None:
             tracks.insert(at_position, track)
@@ -337,6 +337,8 @@ class BasePlaybackController(object):
         self._state = self.STOPPED
         self._shuffled = []
         self._first_shuffle = True
+        self._play_time_accumulated = 0
+        self._play_time_started = None
 
     @property
     def next_track(self):
diff --git a/mopidy/backends/dummy.py b/mopidy/backends/dummy.py
index 0da24c44..b64cdfba 100644
--- a/mopidy/backends/dummy.py
+++ b/mopidy/backends/dummy.py
@@ -36,7 +36,7 @@ class DummyLibraryController(BaseLibraryController):
     find_exact = search
 
 class DummyPlaybackController(BasePlaybackController):
-    def _next(self):
+    def _next(self, track):
         return True
 
     def _pause(self):
@@ -45,7 +45,7 @@ class DummyPlaybackController(BasePlaybackController):
     def _play(self, track):
         return True
 
-    def _previous(self):
+    def _previous(self, track):
         return True
 
     def _resume(self):
diff --git a/mopidy/backends/libspotify.py b/mopidy/backends/libspotify.py
index edffa3af..48c11f4b 100644
--- a/mopidy/backends/libspotify.py
+++ b/mopidy/backends/libspotify.py
@@ -181,6 +181,7 @@ class LibspotifySessionManager(SpotifySessionManager, threading.Thread):
         self.core_queue = core_queue
         self.connected = threading.Event()
         self.audio = AlsaController()
+        self.session = None
 
     def run(self):
         self.connect()
@@ -219,9 +220,11 @@ class LibspotifySessionManager(SpotifySessionManager, threading.Thread):
         """Callback used by pyspotify"""
         logger.debug('Notify main thread')
 
-    def music_delivery(self, *args, **kwargs):
+    def music_delivery(self, session, frames, frame_size, num_frames,
+            sample_type, sample_rate, channels):
         """Callback used by pyspotify"""
-        self.audio.music_delivery(*args, **kwargs)
+        self.audio.music_delivery(session, frames, frame_size, num_frames,
+            sample_type, sample_rate, channels)
 
     def play_token_lost(self, session):
         """Callback used by pyspotify"""
diff --git a/mopidy/mixers/nad.py b/mopidy/mixers/nad.py
index d82a19a3..4aec79cd 100644
--- a/mopidy/mixers/nad.py
+++ b/mopidy/mixers/nad.py
@@ -80,6 +80,7 @@ class NadTalker(BaseProcess):
     def __init__(self, pipe=None):
         super(NadTalker, self).__init__()
         self.pipe = pipe
+        self._device = None
 
     def _run(self):
         self._open_connection()
diff --git a/mopidy/mpd/frontend.py b/mopidy/mpd/frontend.py
index 21d1752b..d7c21a31 100644
--- a/mopidy/mpd/frontend.py
+++ b/mopidy/mpd/frontend.py
@@ -53,6 +53,7 @@ class MpdFrontend(object):
     def __init__(self, backend=None):
         self.backend = backend
         self.command_list = False
+        self.command_list_ok = False
 
     def handle_request(self, request, add_ok=True):
         if self.command_list is not False and request != u'command_list_end':
@@ -286,7 +287,7 @@ class MpdFrontend(object):
             songpos = int(songpos)
             track = self.backend.current_playlist.playlist.tracks[songpos]
             self.backend.current_playlist.remove(track)
-        except IndexError as e:
+        except IndexError:
             raise MpdAckError(u'Position out of bounds')
 
     @handle_pattern(r'^deleteid "(?P<songid>\d+)"$')
diff --git a/mopidy/mpd/server.py b/mopidy/mpd/server.py
index e6abb633..bd37c998 100644
--- a/mopidy/mpd/server.py
+++ b/mopidy/mpd/server.py
@@ -67,15 +67,15 @@ class MpdSession(asynchat.async_chat):
     def found_terminator(self):
         data = ''.join(self.input_buffer).strip()
         self.input_buffer = []
-        input = data.decode(ENCODING)
-        logger.debug(u'Input: %s', indent(input))
-        self.handle_request(input)
+        request = data.decode(ENCODING)
+        logger.debug(u'Input: %s', indent(request))
+        self.handle_request(request)
 
-    def handle_request(self, input):
+    def handle_request(self, request):
         my_end, other_end = multiprocessing.Pipe()
         self.core_queue.put({
             'command': 'mpd_request',
-            'request': input,
+            'request': request,
             'reply_to': pickle_connection(other_end),
         })
         my_end.poll(None)
diff --git a/mopidy/process.py b/mopidy/process.py
index 9459f816..9e260438 100644
--- a/mopidy/process.py
+++ b/mopidy/process.py
@@ -26,6 +26,8 @@ class CoreProcess(BaseProcess):
     def __init__(self, core_queue):
         super(CoreProcess, self).__init__()
         self.core_queue = core_queue
+        self._backend = None
+        self._frontend = None
 
     def _run(self):
         self._setup()