Enhance DataCollector to validate model_reporters functions

mesa/datacollection.py

@@ -134,13 +134,88 @@ def __init__(
             for name, columns in tables.items():
                 self._new_table(name, columns)
 
+    def _validate_model_reporter(self, name, reporter, model):
+        """Validate model reporter and issue warnings if necessary.
+
+        Args:
+            name: Name of the reporter
+            reporter: Reporter definition
+            model: Model instance
+        """
+        # Type 1: Lambda function
+        if isinstance(reporter, types.LambdaType):
+            try:
+                # Try to call the lambda with a model instance
+                reporter(model)
+            except Exception as e:
+                warnings.warn(
+                    f"Warning: Lambda reporter '{name}' failed: {e!s}\n"
+                    f"Example of valid lambda: lambda m: len(m.agents)",
+                    UserWarning,
+                    stacklevel=2,
+                )
+            return
+
+        # Type 2: Method of class/instance
+        if callable(reporter) and not isinstance(reporter, types.LambdaType):
+            try:
+                # Try to call the method
+                reporter(model)
+            except Exception as e:
+                warnings.warn(
+                    f"Warning: Method reporter '{name}' failed: {e!s}\n"
+                    f"Example of valid method: self.get_agent_count or Model.get_agent_count",
+                    UserWarning,
+                    stacklevel=2,
+                )
+            return
+
+        # Type 3: Class attributes (string)
+        if isinstance(reporter, str):
+            if not hasattr(model, reporter):
+                warnings.warn(
+                    f"Warning: Model reporter '{name}' references attribute '{reporter}' "
+                    f"which is not defined in the model.\n"
+                    f"Example of valid attribute: 'model_attribute'",
+                    UserWarning,
+                    stacklevel=2,
+                )
+            return
+
+        # Type 4: Function with parameters in list
+        if isinstance(reporter, list):
+            if not reporter or not callable(reporter[0]):
+                warnings.warn(
+                    f"Warning: Invalid function list format for reporter '{name}'.\n"
+                    f"First element must be a callable function.\n"
+                    f"Example: [function, [param1, param2]]",
+                    UserWarning,
+                    stacklevel=2,
+                )
+            return
+
+        # If none of the above types match
+        warnings.warn(
+            f"Warning: Model reporter '{name}' has invalid type: {type(reporter)}.\n"
+            f"Must be one of:\n"
+            f"1. Lambda function: lambda m: len(m.agents)\n"
+            f"2. Method: self.get_count or Model.get_count\n"
+            f"3. Attribute name (str): 'model_attribute'\n"
+            f"4. Function list: [function, [param1, param2]]",
+            UserWarning,
+            stacklevel=2,
+        )
+
     def _new_model_reporter(self, name, reporter):
         """Add a new model-level reporter to collect.
 
         Args:
             name: Name of the model-level variable to collect.
-            reporter: Attribute string, or function object that returns the
-                      variable when given a model instance.
+            reporter: Can be one of four types:
+                1. Attribute name (str): "attribute_name"
+                2. Lambda function: lambda m: len(m.agents)
+                3. Method: model.get_count or Model.get_count
+                4. List of [function, [parameters]]
         """
         self.model_reporters[name] = reporter
         self.model_vars[name] = []
@@ -263,6 +338,9 @@ def collect(self, model):
         """Collect all the data for the given model object."""
         if self.model_reporters:
             for var, reporter in self.model_reporters.items():
+                # Add validation
+                self._validate_model_reporter(var, reporter, model)
+
                 # Check if lambda or partial function
                 if isinstance(reporter, types.LambdaType | partial):
                     # Use deepcopy to store a copy of the data,