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How can we use opencv in a multistage docker image?

I recently learned about the concept of building docker images based on a multi-staged Dockerfile.
I have been trying simple examples of multi-staged Dockerfiles, and they were working fine. However, when I tried implementing the concept for my own application, I was facing some issues.
My application is about object detection in videos, so I use python and Tensorflow.
Here is my Dockerfile:
FROM python:3-slim AS base
WORKDIR /objectDetector
COPY detect_objects.py .
COPY detector.py .
COPY requirements.txt .
ADD data /objectDetector/data/
ADD models /objectDetector/models/
RUN apt-get update && \
apt-get install protobuf-compiler -y && \
apt-get install ffmpeg libsm6 libxext6 -y && \
apt-get install gcc -y
RUN pip3 install update && python3 -m pip install --upgrade pip
RUN pip3 install tensorflow-cpu==2.9.1
RUN pip3 install opencv-python==4.6.0.66
RUN pip3 install opencv-contrib-python
WORKDIR /objectDetector/models/research
RUN protoc object_detection/protos/*.proto --python_out=.
RUN cp object_detection/packages/tf2/setup.py .
RUN python -m pip install .
RUN python object_detection/builders/model_builder_tf2_test.py
WORKDIR /objectDetector/models/research
RUN pip3 install wheel && pip3 wheel . --wheel-dir=./wheels
FROM python:3-slim
RUN pip3 install update && python3 -m pip install --upgrade pip
COPY --from=base /objectDetector /objectDetector
WORKDIR /objectDetector
RUN pip3 install --no-index --find-links=/objectDetector/models/research/wheels -r requirements.txt
When I try to run my application in the final stage of the container, I receive the following error:
root#3f062f9a5d64:/objectDetector# python detect_objects.py
Traceback (most recent call last):
File "/objectDetector/detect_objects.py", line 3, in <module>
import cv2
ModuleNotFoundError: No module named 'cv2'
So per my understanding, it seems that opencv-python is not successfully moved from the 1st stage to the 2nd.
I have been searching around, and I found some good blogs and questions tackling the issue of multi-staging Dockerfiles, specifically for python libraries. However, it seems I missing something here.
Here are some references that I have been following to solve the issue:
How do I reduce a python (docker) image size using a multi-stage build?
Multi-stage build usage for cuda,cudnn,opencv and ffmpeg #806
So my question is: How can we use opencv in a multistage docker image?

How do I install dateinfer inside my Docker image

Some background : I'm new to understanding docker images and containers and how to write DOCKERFILE. I currently have a Dockerfile which installs all the dependencies that I want through PIP install command and so, it was very simple to build and deploy images.
But I currently have a new requirement to use the Dateinfer module and that cannot be installed through the pip install command.
The repo has to be first cloned and then has to be installed and I'm having difficulty achieving this through a DOCKERFILE. The current work around I've been following for now is to run the container and install it manually in the directory with all the other dependencies and Committing the changes with dateinfer installed.But this is a very tedious and time consuming process and I want to achieve the same by just mentioning it in the DOCKERFILE along with all my other dependencies.
This is what my Dockerfile looks like:
FROM ubuntu:20.04
RUN apt update
RUN apt upgrade -y
RUN apt-get install -y python3
RUN apt-get install -y python3-pip
RUN DEBIAN_FRONTEND=noninteractive TZ=Etc/UTC apt-get -y install tzdata
RUN apt-get install -y libenchant1c2a
RUN apt install git -y
RUN pip3 install argparse
RUN pip3 install boto3
RUN pip3 install numpy==1.19.1
RUN pip3 install scipy
RUN pip3 install pandas
RUN pip3 install scikit-learn
RUN pip3 install matplotlib
RUN pip3 install plotly
RUN pip3 install kaleido
RUN pip3 install fpdf
RUN pip3 install regex
RUN pip3 install pyenchant
RUN pip3 install openpyxl
ADD core.py /
ENTRYPOINT [ "/usr/bin/python3.8", "/core.py”]
So when I try to install Dateinfer like this:
RUN git clone https://github.com/nedap/dateinfer.git
RUN cd dateinfer
RUN pip3 install .
It throws the following error :
ERROR: Directory '.' is not installable. Neither 'setup.py' nor 'pyproject.toml' found.
The command '/bin/sh -c pip3 install .' returned a non-zero code: 1
How do I solve this?

Each RUN directive in a Dockerfile runs in its own subshell. If you write something like this:
RUN cd dateinfer
That is a no-op: it starts a new shell, changes directory, and then the shell exits. When the next RUN command executes, you're back in the / directory.
The easiest way of resolving this is to include your commands in a single RUN statement:
RUN git clone https://github.com/nedap/dateinfer.git && \
cd dateinfer && \
pip3 install .
In fact, you would benefit from doing this with your other pip install commands as well; rather than a bunch of individual RUN
commands, consider instead:
RUN pip3 install \
argparse \
boto3 \
numpy==1.19.1 \
scipy \
pandas \
scikit-learn \
matplotlib \
plotly \
kaleido \
fpdf \
regex \
pyenchant \
openpyxl
That will generally be faster because pip only needs to resolve
dependencies once.
Rather than specifying all the packages individually on the command
line, you could also put them into a requirements.txt file, and then
use pip install -r requirements.txt.

Installing python in Dockerfile without using python image as base

I have a python script that uses DigitalOcean tools (doctl and kubectl) I want to containerize. This means my container will need python, doctl, and kubectl installed. The trouble is, I figure out how to install both python and DigitalOcean tools in the dockerfile.
I can install python using the base image "python:3" and I can also install the DigitalOcean tools using the base image "alpine/doctl". However, the rule is you can only use one base image in a dockerfile.
So I can include the python base image and install the DigitalOcean tools another way:
FROM python:3
RUN <somehow install doctl and kubectl>
RUN pip install firebase-admin
COPY script.py
CMD ["python", "script.py"]
Or I can include the alpine/doctl base image and install python3 another way.
FROM alpine/doctl
RUN <somehow install python>
RUN pip install firebase-admin
COPY script.py
CMD ["python", "script.py"]
Unfortunately, I'm not sure how I would do this. Any help in how I can get all these tools installed would be great!

just add this with any other thing you want to apt-get install:
RUN apt-get update && apt-get install -y \
python3.6 &&\
python3-pip &&\
in alpine it should be something like:
RUN apk add --update --no-cache python3 && ln -sf python3 /usr/bin/python &&\
python3 -m ensurepip &&\
pip3 install --no-cache --upgrade pip setuptools &&\

This Dockerfile worked for me:
FROM alpine/doctl
ENV PYTHONUNBUFFERED=1
RUN apk add --update --no-cache python3 && ln -sf python3 /usr/bin/python
RUN python3 -m ensurepip
RUN pip3 install --no-cache --upgrade pip setuptools
This answer comes from here:(https://stackoverflow.com/a/62555259/7479816; I don't have enough street cred to comment)

You can try multi-stage build as shown below.
Also check your copy statement, you need to define where you want script.py file to be copied as second parameter. "." will copy it to root directory
FROM alpine/doctl
FROM python:3.6-slim-buster
ENV PYTHONUNBUFFERED 1
RUN pip install firebase-admin
COPY script.py .
CMD ["python", "script.py"]

cant install pip in ubuntu 18.04 docker /bin/sh: 1: pip: not found

I am getting the error using pip in my docker image.
FROM ubuntu:18.04
RUN apt-get update && apt-get install -y \
software-properties-common
RUN add-apt-repository universe
RUN apt-get install -y \
python3.6 \
python3-pip
ENV PYTHONUNBUFFERED 1
RUN mkdir /api
WORKDIR /api
COPY . /api/
RUN pip install pipenv
RUN ls
RUN pipenv sync
I installed python 3.6 and pip3 but getting
Step 9/11 : RUN pip install pipenv
---> Running in b184de4eb28e
/bin/sh: 1: pip: not found

To run pip for python3 use pip3, not pip.

Another solution.
You can add this line (after apt-get install). It will upgrade pip to the version you need, for instance:
RUN pip3 install --upgrade pip==20.0.1
and you can then use pip install from requirements file (for instance):
RUN pip install -r requirements.txt

Python in docker container

I am new to Docker so I am sorry for such an easy question.
I am building a docker container which is built on top of a image which is built on ubuntu:vivid image.
When executing my script within the container I am getting an error:
exec: "python": executable file not found in $PATH
How can I solve this?
When I try to run apt-get install python in my Docker file:
FROM my_image # based on ubuntu:vivid
RUN apt-get update && \
apt-get install -y python3
ENV PATH /:$PATH
COPY file.py /
CMD ["python", "file.py", "-h"]
I get:
WARNING: The following packages cannot be authenticated!
libexpat1 libffi6 libmagic1 libmpdec2 libssl1.0.0 libpython3.4-minimal
mime-support libsqlite3-0 libpython3.4-stdlib python3.4-minimal
python3-minimal python3.4 libpython3-stdlib dh-python python3 file
E: There are problems and -y was used without --force-yes
The command '/bin/sh -c apt-get update && apt-get install -y python3' returned a non-zero code: 100
make: *** [image] Error 1
EDIT: added Dockerfile content

You have similar issue with some Linux distribution: "Why am I getting authentication errors for packages from an Ubuntu repository?"
In all cases, the usual sequence of command to install new packages is:
RUN apt-get update -yq && apt-get install -yqq \
git \
python \
...
The OP Ela reports in the comments:
RUN apt-get update -y && apt-get install -y --force-yes \
git \
python \
...

You are installing python3 and then you use the executable of python, I had the same issue and I have resolved using python3.
Try changing your last line of your Dockerfile :
instead of
CMD ["python", "file.py", "-h"]
try :
CMD ["python3", "file.py", "-h"]