Implement empty iterable handling and its corresponding tests in batchrunner.py file.

mesa/batchrunner.py

@@ -106,7 +106,14 @@ def _make_model_kwargs(
     Parameters
     ----------
     parameters : Mapping[str, Union[Any, Iterable[Any]]]
-        Single or multiple values for each model parameter name
+        Single or multiple values for each model parameter name.
+
+        Allowed values for each parameter:
+        - A single value (e.g., `32`, `"relu"`).
+        - A non-empty iterable (e.g., `[0.01, 0.1]`, `["relu", "sigmoid"]`).
+
+        Not allowed:
+        - Empty lists or empty iterables (e.g., `[]`, `()`, etc.). These should be removed manually.
 
     Returns:
     -------
@@ -118,6 +125,12 @@ def _make_model_kwargs(
         if isinstance(values, str):
             # The values is a single string, so we shouldn't iterate over it.
             all_values = [(param, values)]
+        elif isinstance(values, list | tuple | set) and len(values) == 0:
+            # If it's an empty iterable, raise an error
+            raise ValueError(
+                f"Parameter '{param}' contains an empty iterable, which is not allowed."
+            )
+
         else:
             try:
                 all_values = [(param, value) for value in values]

mesa/examples/basic/schelling/agents.py

@@ -6,7 +6,6 @@
 
     def __init__(self, model, agent_type: int) -> None:
         """Create a new Schelling agent.
-
         Args:
             model: The model instance the agent belongs to
             agent_type: Indicator for the agent's type (minority=1, majority=0)
@@ -20,11 +19,23 @@
             self.pos, moore=True, radius=self.model.radius
         )
 
-        # Count similar neighbors
-        similar = sum(neighbor.type == self.type for neighbor in neighbors)
+        valid_neighbors = 0
+        similar_neighbors = 0
+
+        for neighbor in neighbors:
+            if hasattr(neighbor, "type"):  # Exclude empty cells
+                valid_neighbors += 1
+                if neighbor.type == self.type:  # Count similar neighbors
+                    similar_neighbors += 1
+
+        # Calculate the fraction of similar neighbors
+        if valid_neighbors > 0:
+            similarity_fraction = similar_neighbors / valid_neighbors
 
-        # If unhappy, move to a random empty cell:
-        if similar < self.model.homophily:
-            self.model.grid.move_to_empty(self)
+            # If unhappy, move to a random empty cell
+            if similarity_fraction < self.model.homophily:
+                self.model.grid.move_to_empty(self)
+            else:
+                self.model.happy += 1
         else:
             self.model.happy += 1

mesa/examples/basic/schelling/app.py

@@ -26,7 +26,7 @@ def agent_portrayal(agent):
     },
     "density": Slider("Agent density", 0.8, 0.1, 1.0, 0.1),
     "minority_pc": Slider("Fraction minority", 0.2, 0.0, 1.0, 0.05),
-    "homophily": Slider("Homophily", 3, 0, 8, 1),
+    "homophily": Slider("Homophily", 0.3, 0.0, 0.8, 0.1),
     "width": 20,
     "height": 20,
 }

tests/test_batch_run.py

@@ -24,6 +24,37 @@ def test_make_model_kwargs():  # noqa: D103
     assert _make_model_kwargs({"a": "value"}) == [{"a": "value"}]
 
 
+def test_batch_run_with_params_with_empty_content():
+    """Test handling of empty iterables in model kwargs."""
+    # If "a" is a single value and "b" is an empty list (should raise error for the empty list)
+    parameters_with_empty_list = {
+        "a": 3,
+        "b": [],
+    }
+
+    try:
+        _make_model_kwargs(parameters_with_empty_list)
+        raise AssertionError(
+            "Expected ValueError for empty iterable but no error was raised."
+        )
+    except ValueError as e:
+        assert "contains an empty iterable" in str(e)
+
+    # If "a" is a iterable and "b" is an empty list (should still raise error)
+    parameters_with_empty_b = {
+        "a": [1, 2],
+        "b": [],
+    }
+
+    try:
+        _make_model_kwargs(parameters_with_empty_b)
+        raise AssertionError(
+            "Expected ValueError for empty iterable but no error was raised."
+        )
+    except ValueError as e:
+        assert "contains an empty iterable" in str(e)
+
+
 class MockAgent(Agent):
     """Minimalistic agent implementation for testing purposes."""