Update train.py (open-mmlab#428)

* Update train.py

Add user-defined hooks.

* Update train.py

* Update train.py

mmseg/apis/train.py

@@ -5,7 +5,8 @@
 import numpy as np
 import torch
 from mmcv.parallel import MMDataParallel, MMDistributedDataParallel
-from mmcv.runner import build_optimizer, build_runner
+from mmcv.runner import HOOKS, build_optimizer, build_runner
+from mmcv.utils import build_from_cfg
 
 from mmseg.core import DistEvalHook, EvalHook
 from mmseg.datasets import build_dataloader, build_dataset
@@ -113,6 +114,20 @@ def train_segmentor(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: