fix logic issues in predprey example

Ensure prey (1) have children, which (2) aren’t predators

Author: JostMigenda

episodes/files/pred-prey/predprey.py

@@ -51,11 +51,7 @@ def avoid_predators(self, predator_list):
 
         # Add a steering factor away from each predator. Strength increases with closeness.
         for predator in predator_list:
-            # Fetch location of predator
-            predator_x = self.x;
-            predator_y = self.y;
-
-            # Check if the two predators are within interaction radius
+            # Check if predator and prey are within interaction radius
             dx = self.x - predator.x
             dy = self.y - predator.y
             distance = math.sqrt(dx * dx + dy * dy)
@@ -159,6 +155,7 @@ def reproduce(self):
             child.vx = np.random.uniform() * 2 - 1
             child.vy = np.random.uniform() * 2 - 1
             child.life = self.life
+            return child
 
 
 class Predator:
@@ -304,7 +301,7 @@ def eaten(self, prey_list):
 
 class Model:
 
-    def __init__(self, steps = 250):
+    def __init__(self, steps = 50):
         self.steps = steps
         self.num_prey = 200
         self.num_predators = 50
@@ -373,7 +370,7 @@ def _step(self):
             c = p.reproduce()
             if c:
                 children.append(c)
-        self.predators.extend(children)
+        self.prey.extend(children)
         children = []
         for p in self.predators:
             c = p.reproduce()