Can't install OpenCV python3.8

Try to upgrade your pip with

pip install --upgrade pip

and then run the

pip install opencv-python

Installation and Usage guide on pypi web site says

Pip install fails with ModuleNotFoundError: No module named 'skbuild'?

Since opencv-python version 4.3.0.*, manylinux1 wheels were replaced by manylinux2014 wheels. If your pip is too old, it will try to use the new source distribution introduced in 4.3.0.38 to manually build OpenCV because it does not know how to install manylinux2014 wheels. However, source build will also fail because of too old pip because it does not understand build dependencies in pyproject.toml. To use the new manylinux2014 pre-built wheels (or to build from source), your pip version must be >= 19.3.
Please upgrade pip with
pip install --upgrade pip

I was facing this similar situation:

Dockerfile:

FROM nvidia/cuda:10.0-cudnn7-runtime-ubuntu18.04

RUN apt-get update -y
RUN apt-get install -y vim curl iputils-ping python3-dev python3-pip libsm6 
libxext6 libxrender-dev python3.6
RUN pip3 install -r /requirements.txt
...

requirements.txt:

...
opencv-python
...

Upon running docker-compose up &, I was receiving this error:

 Traceback (most recent call last):
   File "<string>", line 1, in <module>
   File "/tmp/pip-build-acog3xol/opencv-python/setup.py", line 9, in <module>
     import skbuild
 ModuleNotFoundError: No module named 'skbuild'

I tried the suggested solutions of upgrading pip3 but was getting the same problem.

What worked for me was fixing the opencv-python version in requirements.txt. Previously, it was pulling version 4.4.0.40. I instead changed requirements.txt to:

...
opencv-python==4.2.0.34
...