add comments

product.py

@@ -9,6 +9,7 @@ class ProductAgent(ap.Agent):
         self.name = name
 
     def a_successors(self):
+        # find successors of a product, return in AgentList (ProductAgent)
         nodes = self.product_network.graph.successors(
             self.product_network.positions[self])
         return ap.AgentList(
@@ -16,6 +17,7 @@ class ProductAgent(ap.Agent):
             [ap.AgentIter(self.model, node).to_list()[0] for node in nodes])
 
     def a_predecessors(self):
+        # find predecessors of a product, return in AgentList (ProductAgent)
         nodes = self.product_network.graph.predecessors(
             self.product_network.positions[self])
         return ap.AgentList(