[experiments][api] Refactor filter usage

Use list comprehension and sets.

beat/web/experiments/api.py

@@ -102,7 +102,7 @@ class ListCreateExperimentsView(ListCreateContributionView):
 
     def get(self, request, author_name):
         def _getStatusLabel(status):
-            return filter(lambda x: x[0] == status, Experiment.STATUS)[0][1]
+            return [s for s in Experiment.STATUS if s[0] == status][0][1]
 
         def _custom_compare(exp1, exp2):
             PENDING = _getStatusLabel(Experiment.PENDING)
@@ -134,8 +134,8 @@ class ListCreateExperimentsView(ListCreateContributionView):
         # Retrieve the experiments
         fields_to_return_original = self.get_serializer_fields(request)
 
-        fields_to_return = fields_to_return_original + filter(lambda x: x not in fields_to_return_original,
-                                                              ['status', 'creation_date', 'start_date', 'end_date'])
+        mandatory_fields = set(['status', 'creation_date', 'start_date', 'end_date'])
+        fields_to_return = list(mandatory_fields.union(fields_to_return_original))
 
         experiments = self.model.objects.from_author_and_public(request.user, author_name).select_related()