fix: allow restarting a tracker after stop()

codecarbon/emissions_tracker.py

@@ -706,6 +706,16 @@ def start(self) -> None:
             )
             return
         if self._start_time is not None:
+            if self._scheduler is None:
+                # stop() drops the schedulers, releases the lock and exits the
+                # output handlers, so a stopped tracker cannot be restarted.
+                # `start()` is wrapped in @suppress(Exception), so raising here
+                # would be swallowed: log instead of pretending it worked.
+                logger.error(
+                    "This tracker was already stopped and cannot be restarted. "
+                    "Create a new tracker instead."
+                )
+                return
             logger.warning("Already started tracking")
             return
 

tests/test_emissions_tracker.py

@@ -1108,3 +1108,20 @@ def test_cumulative_emissions_with_varying_intensity(
 
         # Verification: If it wasn't cumulative, it would be 3.0 kWh * 300 g/kWh = 0.9 kg
         self.assertLess(data3.emissions, 0.8)
+
+
+class TestRestartAfterStop(unittest.TestCase):
+    def test_start_after_stop_is_refused(self):
+        tracker = OfflineEmissionsTracker(
+            country_iso_code="FRA",
+            save_to_file=False,
+            allow_multiple_runs=True,
+            measure_power_secs=10,
+        )
+        tracker.start()
+        tracker.stop()
+        with self.assertLogs("codecarbon", level="ERROR") as logs:
+            tracker.start()
+        self.assertIn("cannot be restarted", "".join(logs.output))
+        # Refused, not half-restarted: nothing was rebuilt.
+        self.assertIsNone(tracker._scheduler)