Bugfixes to DEVS (#2478)

benchmarks/global_benchmark.py

@@ -33,7 +33,6 @@ def run_model(model_class, seed, parameters):
     if model_class.__name__ in uses_simulator:
         simulator = ABMSimulator()
         model = model_class(simulator=simulator, seed=seed, **parameters)
-        simulator.setup(model)
     else:
         model = model_class(seed=seed, **parameters)
 

mesa/examples/advanced/wolf_sheep/model.py

@@ -61,12 +61,13 @@ def __init__(
             simulator: ABMSimulator instance for event scheduling
         """
         super().__init__(seed=seed)
+        self.simulator = simulator
+        self.simulator.setup(self)
 
         # Initialize model parameters
         self.height = height
         self.width = width
         self.grass = grass
-        self.simulator = simulator
 
         # Create grid using experimental cell space
         self.grid = OrthogonalVonNeumannGrid(

mesa/experimental/devs/simulator.py

@@ -57,8 +57,20 @@ def setup(self, model: Model) -> None:
         Args:
             model (Model): The model to simulate
 
+        Raises:
+            Exception if simulator.time is not equal to simulator.starttime
+            Exception if event list is not empty
+
         """
-        self.event_list.clear()
+        if self.time != self.start_time:
+            raise ValueError(
+                "trying to setup model, but current time is not equal to start_time, Has the simulator been reset or freshly initialized?"
+            )
+        if not self.event_list.is_empty():
+            raise ValueError(
+                "trying to setup model, but events have already been scheduled. Call simulator.setup before any scheduling"
+            )
+
         self.model = model
 
     def reset(self):
@@ -68,7 +80,20 @@ def reset(self):
         self.time = self.start_time
 
     def run_until(self, end_time: int | float) -> None:
-        """Run the simulator until the end time."""
+        """Run the simulator until the end time.
+
+        Args:
+            end_time (int | float): The end time for stopping the simulator
+
+        Raises:
+            Exception if simulator.setup() has not yet been called
+
+        """
+        if self.model is None:
+            raise Exception(
+                "simulator has not been setup, call simulator.setup(model) first"
+            )
+
         while True:
             try:
                 event = self.event_list.pop_event()
@@ -84,6 +109,26 @@ def run_until(self, end_time: int | float) -> None:
                 self._schedule_event(event)  # reschedule event
                 break
 
+    def run_next_event(self):
+        """Execute the next event.
+
+        Raises:
+            Exception if simulator.setup() has not yet been called
+
+        """
+        if self.model is None:
+            raise Exception(
+                "simulator has not been setup, call simulator.setup(model) first"
+            )
+
+        try:
+            event = self.event_list.pop_event()
+        except IndexError:  # event list is empty
+            return
+        else:
+            self.time = event.time
+            event.execute()
+
     def run_for(self, time_delta: int | float):
         """Run the simulator for the specified time delta.
 
@@ -92,6 +137,7 @@ def run_for(self, time_delta: int | float):
                                      plus the time delta
 
         """
+        # fixme, raise initialization error or something like it if model.setup has not been called
         end_time = self.time + time_delta
         self.run_until(end_time)
 
@@ -228,7 +274,7 @@ def setup(self, model):
 
         """
         super().setup(model)
-        self.schedule_event_now(self.model.step, priority=Priority.HIGH)
+        self.schedule_event_next_tick(self.model.step, priority=Priority.HIGH)
 
     def check_time_unit(self, time) -> bool:
         """Check whether the time is of the correct unit.
@@ -277,14 +323,24 @@ def run_until(self, end_time: int) -> None:
         Args:
             end_time (float| int): The end_time delta. The simulator is until the specified end time
 
+        Raises:
+            Exception if simulator.setup() has not yet been called
+
         """
+        if self.model is None:
+            raise Exception(
+                "simulator has not been setup, call simulator.setup(model) first"
+            )
+
         while True:
             try:
                 event = self.event_list.pop_event()
             except IndexError:
                 self.time = end_time
                 break
 
+            # fixme: the alternative would be to wrap model.step with an annotation which
+            #  handles this scheduling.
             if event.time <= end_time:
                 self.time = event.time
                 if event.fn() == self.model.step:
@@ -298,17 +354,6 @@ def run_until(self, end_time: int) -> None:
                 self._schedule_event(event)
                 break
 
-    def run_for(self, time_delta: int):
-        """Run the simulator for the specified time delta.
-
-        Args:
-            time_delta (float| int): The time delta. The simulator is run from the current time to the current time
-                                     plus the time delta
-
-        """
-        end_time = self.time + time_delta - 1
-        self.run_until(end_time)
-
 
 class DEVSimulator(Simulator):
     """A simulator where the unit of time is a float.

tests/test_devs.py

@@ -1,6 +1,6 @@
 """Tests for experimental Simulator classes."""
 
-from unittest.mock import MagicMock
+from unittest.mock import MagicMock, Mock
 
 import pytest
 
@@ -55,6 +55,23 @@ def test_devs_simulator():
     with pytest.raises(ValueError):
         simulator.schedule_event_absolute(fn2, 0.5)
 
+    # step
+    simulator = DEVSimulator()
+    model = MagicMock(spec=Model)
+    simulator.setup(model)
+
+    fn = MagicMock()
+    simulator.schedule_event_absolute(fn, 1.0)
+    simulator.run_next_event()
+    fn.assert_called_once()
+    assert simulator.time == 1.0
+    simulator.run_next_event()
+    assert simulator.time == 1.0
+
+    simulator = DEVSimulator()
+    with pytest.raises(Exception):
+        simulator.run_next_event()
+
     # cancel_event
     simulator = DEVSimulator()
     model = MagicMock(spec=Model)
@@ -70,6 +87,24 @@ def test_devs_simulator():
     assert simulator.model is None
     assert simulator.time == 0.0
 
+    # run without setup
+    simulator = DEVSimulator()
+    with pytest.raises(Exception):
+        simulator.run_until(10)
+
+    # setup with time advanced
+    simulator = DEVSimulator()
+    simulator.time = simulator.start_time + 1
+    model = MagicMock(spec=Model)
+    with pytest.raises(Exception):
+        simulator.setup(model)
+
+    # setup with event scheduled
+    simulator = DEVSimulator()
+    simulator.schedule_event_now(Mock())
+    with pytest.raises(Exception):
+        simulator.setup(model)
+
 
 def test_abm_simulator():
     """Tests abm simulator."""
@@ -86,7 +121,12 @@ def test_abm_simulator():
 
     simulator.run_for(3)
     assert model.step.call_count == 3
-    assert simulator.time == 2
+    assert simulator.time == 3
+
+    # run without setup
+    simulator = ABMSimulator()
+    with pytest.raises(Exception):
+        simulator.run_until(10)
 
 
 def test_simulation_event():

tests/test_examples.py

@@ -69,6 +69,5 @@ def test_wolf_sheep():  # noqa: D103
     from mesa.experimental.devs import ABMSimulator
 
     simulator = ABMSimulator()
-    model = WolfSheep(seed=42, simulator=simulator)
-    simulator.setup(model)
+    WolfSheep(seed=42, simulator=simulator)
     simulator.run_for(10)