find_next_active_node: take min outside lsit comprehension

Author: geraintpalmer

ciw/simulation.py

@@ -171,9 +171,9 @@ def find_next_active_node(self):
         """
         Returns the next active node:
         """
+        next_event_date = min([nd.next_event_date for nd in self.nodes])
         next_active_node_indices = [i for i, x in enumerate([
-            nd.next_event_date for nd in self.nodes]) if x == min([
-            nd.next_event_date for nd in self.nodes])]
+            nd.next_event_date for nd in self.nodes]) if x == next_event_date]
         if len(next_active_node_indices) > 1:
             return self.nodes[random_choice(next_active_node_indices)]
         return self.nodes[next_active_node_indices[0]]