[Fix] Fix conflict of resume argument (#2224)

* fix `resume` error

* fix

tools/train.py

@@ -27,8 +27,12 @@ def parse_args():
         help='enable automatically scaling LR.')
     parser.add_argument(
         '--resume',
-        action='store_true',
-        help='resume from the latest checkpoint in the work_dir automatically')
+        nargs='?',
+        type=str,
+        const='auto',
+        help='If specify checkpoint path, resume from it, while if not '
+        'specify, try to auto resume from the latest checkpoint '
+        'in the work directory.')
     parser.add_argument(
         '--ceph', action='store_true', help='Use ceph as data storage backend')
     parser.add_argument(
@@ -105,7 +109,14 @@ def main():
                                '"auto_scale_lr.enable" or '
                                '"auto_scale_lr.base_batch_size" in your'
                                ' configuration file.')
-    cfg.resume = args.resume
+
+    # resume is determined in this priority: resume from > auto_resume
+    if args.resume == 'auto':
+        cfg.resume = True
+        cfg.load_from = None
+    elif args.resume is not None:
+        cfg.resume = True
+        cfg.load_from = args.resume
 
     # build the runner from config
     if 'runner_type' not in cfg: