[Feature]: Add param scheduler hook (#63)

* [Feature]: Add param scheduler hook

* [Fix]: update docstring and add assert_call to UT

mmengine/hooks/__init__.py

@@ -2,5 +2,8 @@
 from .hook import Hook
 from .iter_timer_hook import IterTimerHook
 from .sampler_seed_hook import DistSamplerSeedHook
+from .param_scheduler_hook import ParamSchedulerHook
 
-__all__ = ['Hook', 'IterTimerHook', 'DistSamplerSeedHook']
+__all__ = [
+    'Hook', 'IterTimerHook', 'DistSamplerSeedHook', 'ParamSchedulerHook'
+]

mmengine/hooks/param_scheduler_hook.py

+# Copyright (c) OpenMMLab. All rights reserved.
+from typing import Optional, Sequence
+
+from mmengine.data import BaseDataSample
+from mmengine.registry import HOOKS
+from .hook import Hook
+
+
+@HOOKS.register_module()
+class ParamSchedulerHook(Hook):
+    """A hook to update some hyper-parameters in optimizer, e.g learning rate
+    and momentum."""
+
+    def after_iter(self,
+                   runner: object,
+                   data_batch: Optional[Sequence[BaseDataSample]] = None,
+                   outputs: Optional[Sequence[BaseDataSample]] = None) -> None:
+        """Call step function for each scheduler after each iteration.
+
+        Args:
+            runner (object): The runner of the training process.
+            data_batch (Sequence[BaseDataSample]): Data from dataloader. In
+                order to keep this interface consistent with other hooks, we
+                keep ``data_batch`` here. Defaults to None.
+            outputs (Sequence[BaseDataSample]): Outputs from model. In
+                order to keep this interface consistent with other hooks, we
+                keep ``data_batch`` here. Defaults to None.
+        """
+        for scheduler in runner.schedulers:  # type: ignore
+            if not scheduler.by_epoch:
+                scheduler.step()
+
+    def after_epoch(self, runner: object) -> None:
+        """Call step function for each scheduler after each epoch.
+
+        Args:
+            runner (object): The runner of the training process.
+        """
+        for scheduler in runner.schedulers:  # type: ignore
+            if scheduler.by_epoch:
+                scheduler.step()

tests/test_hook/test_param_scheduler_hook.py

+# Copyright (c) OpenMMLab. All rights reserved.
+from unittest.mock import Mock
+
+from mmengine.hooks import ParamSchedulerHook
+
+
+class TestParamSchedulerHook:
+
+    def test_after_iter(self):
+        Hook = ParamSchedulerHook()
+        Runner = Mock()
+        scheduler = Mock()
+        scheduler.step = Mock()
+        scheduler.by_epoch = False
+        Runner.schedulers = [scheduler]
+        Hook.after_iter(Runner)
+        scheduler.step.assert_called()
+
+    def test_after_epoch(self):
+        Hook = ParamSchedulerHook()
+        Runner = Mock()
+        scheduler = Mock()
+        scheduler.step = Mock()
+        scheduler.by_epoch = True
+        Runner.schedulers = [scheduler]
+        Hook.after_epoch(Runner)
+        scheduler.step.assert_called()