cannot import OpenCV in a Docker container in Raspberry Pi

I am trying to build a Docker container in Raspbian 10.

FROM python:3.5-busterRUN apt-get updateRUN apt-get install apt-utils -yRUN apt-get install python-opencv -yRUN apt-get install python3-opencv -yCOPY a.py /CMD ["python3", "a.py"]

a.py is simply import cv2

When I run the container, I got the following errors.

Traceback (most recent call last):  File "a.py", line 1, in <module>    import cv2ImportError: No module named 'cv2'