[Refactor] Remove some code in mmdet/apis/train.py (open-mmlab#6576)

* remove some code about custom hooks in apis/train.py

* files were modified by yapf

mmdet/apis/train.py

@@ -6,10 +6,9 @@
 import torch
 import torch.distributed as dist
 from mmcv.parallel import MMDataParallel, MMDistributedDataParallel
-from mmcv.runner import (HOOKS, DistSamplerSeedHook, EpochBasedRunner,
+from mmcv.runner import (DistSamplerSeedHook, EpochBasedRunner,
                          Fp16OptimizerHook, OptimizerHook, build_optimizer,
                          build_runner, get_dist_info)
-from mmcv.utils import build_from_cfg
 
 from mmdet.core import DistEvalHook, EvalHook
 from mmdet.datasets import (build_dataloader, build_dataset,
@@ -163,9 +162,14 @@ def train_detector(model,
         optimizer_config = cfg.optimizer_config
 
     # register hooks
-    runner.register_training_hooks(cfg.lr_config, optimizer_config,
-                                   cfg.checkpoint_config, cfg.log_config,
-                                   cfg.get('momentum_config', None))
+    runner.register_training_hooks(
+        cfg.lr_config,
+        optimizer_config,
+        cfg.checkpoint_config,
+        cfg.log_config,
+        cfg.get('momentum_config', None),
+        custom_hooks_config=cfg.get('custom_hooks', None))
+
     if distributed:
         if isinstance(runner, EpochBasedRunner):
             runner.register_hook(DistSamplerSeedHook())
@@ -193,20 +197,6 @@ def train_detector(model,
         runner.register_hook(
             eval_hook(val_dataloader, **eval_cfg), priority='LOW')
 
-    # user-defined hooks
-    if cfg.get('custom_hooks', None):
-        custom_hooks = cfg.custom_hooks
-        assert isinstance(custom_hooks, list), \
-            f'custom_hooks expect list type, but got {type(custom_hooks)}'
-        for hook_cfg in cfg.custom_hooks:
-            assert isinstance(hook_cfg, dict), \
-                'Each item in custom_hooks expects dict type, but got ' \
-                f'{type(hook_cfg)}'
-            hook_cfg = hook_cfg.copy()
-            priority = hook_cfg.pop('priority', 'NORMAL')
-            hook = build_from_cfg(hook_cfg, HOOKS)
-            runner.register_hook(hook, priority=priority)
-
     if cfg.resume_from:
         runner.resume(cfg.resume_from)
     elif cfg.load_from: