Merge pull request #1620 from kingosticks/fix/library_lookup_empty_uris

Fix library.lookup with an empty uri list

mopidy/core/library.py

@@ -228,8 +228,9 @@ class LibraryController(object):
 
         # TODO: lookup(uris) to backend APIs
         for backend, backend_uris in self._get_backends_to_uris(uris).items():
-            for u in backend_uris:
-                futures[(backend, u)] = backend.library.lookup(u)
+            if backend_uris:
+                for u in backend_uris:
+                    futures[(backend, u)] = backend.library.lookup(u)
 
         for (backend, u), future in futures.items():
             with _backend_error_handling(backend):

tests/core/test_library.py

@@ -148,6 +148,9 @@ class CoreLibraryTest(BaseCoreLibraryTest):
             Ref.track(uri='dummy1:track:/foo/baz.mp3', name='Baz'),
         ])
 
+    def test_lookup_returns_empty_dict_for_no_uris(self):
+        self.assertEqual({}, self.core.library.lookup(uris=[]))
+
     def test_lookup_fails_with_uri_and_uris_set(self):
         with self.assertRaises(ValueError):
             self.core.library.lookup('dummy1:a', ['dummy2:a'])