Fix bug that prey might be placed elsewhere when prey's collision detection is done before snake's collision detection: Replace prey in following update step and not during collision detection.

snake/prey.py

@@ -8,26 +8,33 @@ class Prey(GameObject):
         self.__bounding_box = pygame.rect.Rect(0, 0, size, size)
         self.__color = color
         self.__window_size = window_size
+        self.__next_pos = None
         self.__place_randomly()
     
     def __place_randomly(self) -> None:
-        self.__bounding_box.center = [random.randint(0, max_val) 
-                                      for max_val in self.__window_size]
+        self.__next_pos = [random.randint(0, max_val) 
+                           for max_val in self.__window_size]
 
 
-    def __collides_with_other(self, game_objs: list[GameObject]) -> bool:
+    def __collides_with_other(self, pos: tuple, game_objs: list[GameObject]) -> bool:
+        box = pygame.rect.Rect(self.__bounding_box)
+        box.center = pos
+        
         for obj in game_objs:
-            if not isinstance(obj, Prey) and self.get_bounding_boxes()[0].collidelist(obj.get_bounding_boxes()) > -1:
+            if not isinstance(obj, Prey) and box.collidelist(obj.get_bounding_boxes()) > -1:
                 return True
+    
 
     def draw(self, surface: pygame.surface.Surface) -> None:
         pygame.draw.rect(surface, color=self.__color, rect=self.__bounding_box)
 
 
     def update(self, user_input: int, game_objs: list[GameObject]):
-        while self.__collides_with_other(game_objs):
-            self.__place_randomly()
-            
+        self.__bounding_box.center = self.__next_pos
+
+        while self.__collides_with_other(self.__next_pos, game_objs):
+            self.__place_randomly()    
+    
 
     def get_bounding_boxes(self) -> list[pygame.rect.Rect]:
         return [self.__bounding_box]