fix: position_agent: Enforce type of x and y

examples/schelling/model.py

@@ -70,7 +70,7 @@ def __init__(self, width=20, height=20, density=0.8, minority_pc=0.2, homophily=
                     agent_type = 0
 
                 agent = SchellingAgent((x, y), self, agent_type)
-                self.grid.position_agent(agent, (x, y))
+                self.grid.position_agent(agent, x, y)
                 self.schedule.add(agent)
 
         self.running = True

mesa/space.py

@@ -484,6 +484,17 @@ def position_agent(
         If x or y are positive, they are used.
         Use 'swap_pos()' to swap agents positions.
         """
+        if not (isinstance(x, int) or x == "random"):
+            raise Exception(
+                "x must be an integer or a string 'random'."
+                f" Actual type: {type(x)}. Actual value: {x}."
+            )
+        if not (isinstance(y, int) or y == "random"):
+            raise Exception(
+                "y must be an integer or a string 'random'."
+                f" Actual type: {type(y)}. Actual value: {y}."
+            )
+
         if x == "random" or y == "random":
             if len(self.empties) == 0:
                 raise Exception("ERROR: Grid full")

tests/test_grid.py

@@ -232,6 +232,25 @@ def setUp(self):
                 self.grid.place_agent(a, (x, y))
         self.num_agents = len(self.agents)
 
+    @patch.object(MockAgent, "model", create=True)
+    def test_position_agent(self, mock_model):
+        a = MockAgent(100, None)
+        with self.assertRaises(Exception) as exc_info:
+            self.grid.position_agent(a, (1, 1))
+        expected = (
+            "x must be an integer or a string 'random'."
+            " Actual type: <class 'tuple'>. Actual value: (1, 1)."
+        )
+        assert str(exc_info.exception) == expected
+        with self.assertRaises(Exception) as exc_info:
+            self.grid.position_agent(a, "(1, 1)")
+        expected = (
+            "x must be an integer or a string 'random'."
+            " Actual type: <class 'str'>. Actual value: (1, 1)."
+        )
+        assert str(exc_info.exception) == expected
+        self.grid.position_agent(a, "random")
+
     @patch.object(MockAgent, "model", create=True)
     def test_enforcement(self, mock_model):
         """