Train error，maybe something wrong in bounding_box.py

[Aliengmx]

@mjanusz Hi, if I used python2.7 I got the same syntax error with https://github.com/google/ffn/issues/19. And then I transform to python 3.7 I got another new error: def _required(bbox: Optional[BoundingBox]) -> BoundingBox: NameError: name 'Optional' is not defined

Is any help for this issue?

[oradomskyi]

Hi @Aliengmx

add import line below to the beginning of file bounding_box.py

from typing import Optional