not valid dir

[bryanbocao]

Error when running

python3 coco_download.py --annotation train2017_mini_25k.json --output train2017_mini_25k

Traceback (most recent call last):
  File "coco_download.py", line 23, in <module>
    assert pathlib.Path(args.output_dir).is_dir(), "not valid dir"
AssertionError: not valid dir