Add more error info in build_from_cfg (#834)

* Add more Error info in building from config

* Add more Error info in building from config

* change error info

mmcv/utils/registry.py

@@ -175,5 +175,8 @@ def build_from_cfg(cfg, registry, default_args=None):
     else:
         raise TypeError(
             f'type must be a str or valid type, but got {type(obj_type)}')
-
+    try:
         return obj_cls(**args)
+    except Exception as e:
+        # Normal TypeError does not print class name.
+        raise type(e)(f'{obj_cls.__name__}: {e}')

tests/test_utils/test_registry.py

@@ -221,3 +221,8 @@ def test_build_from_cfg():
     with pytest.raises(TypeError):
         cfg = dict(type='ResNet', depth=50)
         model = mmcv.build_from_cfg(cfg, BACKBONES, default_args=0)
+
+    # incorrect arguments
+    with pytest.raises(TypeError):
+        cfg = dict(type='ResNet', non_existing_arg=50)
+        model = mmcv.build_from_cfg(cfg, BACKBONES)