first try on a combined sensors class

slic/core/sensor/combined.py

@@ -0,0 +1,37 @@
+from .sensor import Sensor
+
+
+class Combined(Sensor):
+
+    def __init__(self, ID, sensors, combination, **kwargs):
+        super().__init__(ID, **kwargs)
+        self.sensors = sensors
+        self.combination = combination
+        #TODO: not sure how to handle the following
+        del self.aggregation
+        del self._cache
+
+
+    def start(self):
+        for s in self.sensors:
+            s.start()
+
+    def stop(self):
+        for s in self.sensors:
+            s.stop()
+
+
+    def get_current_value(self):
+        values = (s.get_current_value() for s in self.sensors)
+        return self.combination(*values)
+
+    def get_last_value(self):
+        values = (s.get_last_value() for s in self.sensors)
+        return self.combination(*values)
+
+    def get_aggregate(self):
+        values = (s.get_aggregate() for s in self.sensors)
+        return self.combination(*values)
+
+
+