cannot import OpenCV in a Docker container in Raspberry Pi

Question

I am trying to build a Docker container that can run Python OpenCV code in Raspbian 10.

FROM python:3.5-buster
RUN apt-get update
RUN apt-get install apt-utils -y
RUN apt-get install python-opencv -y
RUN apt-get install python3-opencv -y
COPY 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 cv2
ImportError: No module named 'cv2'

Answer 1

Three workarounds:

• Use debian:buster as your base container instead of python:3.5-buster

or

• Put this into your Dockerfile:

ENV PYTHONPATH /usr/lib/python3/dist-packages

or

• Similarly, put this at the top of a.py:

import sys
sys.path.append('/usr/lib/python3/dist-packages')

import cv2

It's unclear why Python's package path system is so fragile, but the last two are a variation of suggestions on a similar question^[1], and among the quickest workarounds I could verify.

^[1] Cannot find module cv2 when using OpenCV