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Dockerfile: /bin/sh: 1: apt-get: not found

When building a Docker file, I get the error
"/bin/sh: 1: apt-get: not found"
docker file:
FROM python:3.8
FROM ubuntu:20.04
ENV PATH="/env/bin/activate"
RUN apt-get update -y && apt-get upgrade -y
WORKDIR /var/www/html/
COPY . .
RUN pip install -r requirements.txt
EXPOSE 8000
CMD ["python", "manage.py"]

You are setting the PATH to /env/bin/activate and that is then the only place where apt-get is searched for. There is no need to activate a virtual env inside the container, just get rid of that line. pip can install the packages in requirements.txt to the "system" Python without issues.
You cannot layer 2 images like you are attempting to do, with multiple FROM statements. Just use FROM python:3.8 and drop the ubuntu. Multiple FROM statements are used in multi-stage builds where you have intermediate images which produce artifacts that are copied to the final image.
So just do:
FROM python:3.8
RUN apt-get update -y && apt-get upgrade -y
WORKDIR /var/www/html/
COPY . .
RUN pip install -r requirements.txt
EXPOSE 8000
CMD ["python", "manage.py"]
.. although why you would put Python code in /var/www/html beats me. Probably you don't.

How to invalidate Dockerfile cache when pip installing from repo

I have a Dockerfile that needs to install the latest package code from a private git repo, however because the dockerfile/url/commit doesn't change (I just follow the latest in master), Docker will cache this request and won't pull the latest code.
I can disable build caching entirely which fixes the issue - but this results in a slow build.
How can I just force docker not to use the cache for the one command?
FROM tiangolo/uvicorn-gunicorn-fastapi:python3.7
COPY ./requirements.txt /app
RUN pip install --upgrade pip
RUN pip install -r requirements.txt
# This needs to be separate to trigger to invalidate the build cache
RUN pip install -e git+https://TOKEN#github.com/user/private-package.git#egg=private_package
COPY ./main.py /app
COPY ./app /app/app

Add
ARG foo=bar
Before RUN pip install -e ... in your docker file.
Then in your script with docker build .... add as a parameter
--build-arg foo="$(date -s)"

Python package not installable in docker container

I have basic python docker container file like this:
FROM python:3.8
RUN pip install --upgrade pip
EXPOSE 8000
ENV PYTHONDONTWRITEBYTECODE=1
# Turns off buffering for easier container logging
ENV PYTHONUNBUFFERED=1
# Install pip requirements
COPY requirements.txt .
RUN python -m pip install -r requirements.txt
WORKDIR /app
COPY . /app
RUN useradd appuser && chown -R appuser /app
USER appuser
CMD ["gunicorn", "--bind", "0.0.0.0:8000", "app:app"]
I want to run my flask application in a docker container by using this definition file. Locally I can start a new virtual env, install everything via pip install -r requirements.txt on python 3.8 and it does not fail.
When building the docker image it fails to install all packages from the requirements.txt. For example this package fails:
ERROR: Could not find a version that satisfies the requirement cvxopt==1.2.5.post1
ERROR: No matching distribution found for cvxopt==1.2.5.post1
When I comment out the package in the requirements.txt everything seems to work. The package itself claims to be compatible with python >2.7. Same behavior for the package pywin32==228 here.

Looing at the wheel files in the package, cvxopt.1.2.5.post1 only contains a build for Windows. For Linux (such as the docker container), you should use cvxopt.1.2.5.

You should replace the version with 1.2.5 (pip install cvxopt==1.2.5)
The latest version cvxopt 1.2.5.post1 is not compatible with all architectures: https://pypi.org/project/cvxopt/1.2.5.post1/#files
The previous one is compatible with a lot more hardware and should be able to run on your Docker image: https://pypi.org/project/cvxopt/1.2.5/#files

Why does installing `install_requires` from setup.py using a dot "." in the requirements.txt fail in Dockerfile?

I am trying to use the method described here
Dockerfile
FROM python:3.8
COPY requirements.txt setup.py /tmp/
RUN pip3 install -r /tmp/requirements.txt \
&& rm /tmp/*
this fails with:
Step 1/7 : FROM python:3.8
---> 79cc46abd78d
Step 2/7 : COPY requirements.txt setup.py /tmp/
---> Using cache
---> a50a0a8ecb06
Step 3/7 : RUN pip3 install -r /tmp/requirements.txt && rm /tmp/*
---> Running in c7d29bd8f23c
ERROR: Directory '.' is not installable. Neither 'setup.py' nor 'pyproject.toml'
found.
I also tried commenting out the RUN command, entering the container and running
pip3 install -r /tmp/requirements.txt manually. This worked without error.
I have no idea what might be the issue here.

I figured it out:
the dot . is not relative to the requirements.txt but rather to the current working directory. The reason it worked when I did it manually is, that I also mounted my workspace into a devcontainer and had my working directory in this workspace which also contained the setup.py
The solution is thus to do something like this:
WORKDIR /tmp
COPY requirements.txt setup.py ./
RUN pip3 install -r requirements.txt \
&& rm /tmp/*

Why Docker does not find Flask Module

I've created flask app and try to dockerize it. It uses machine learning libraries, I had some problems with download it so my Dockerfile is a little bit messy, but Image was succesfully created.
from alpine:latest
RUN apk add --no-cache python3-dev \
&& pip3 install --upgrade pip
WORKDIR /app
COPY . /app
FROM python:3.5
RUN pip3 install gensim
RUN pip3 freeze > requirements.txt
RUN pip3 --no-cache-dir install -r requirements.txt
EXPOSE 5000
ENV PATH=/venv/bin:$PATH
ENV FLASK_APP /sentiment-service/__init__.py
CMD ["python","-m","flask", "run", "--host", "0.0.0.0", "--port", "5000"]
and when i try:
docker run my_app:latest
I get
/usr/local/bin/python: No module named flask
Of course I have Flask==1.1.1 in my requirements.txt file.
Thanks for any help!

The problem is here:
RUN pip3 freeze > requirements.txt
The > operator in bash overwrites the content of the file. If you want to append to your requirements.txt, consider using >> operator:
RUN pip3 freeze >> requirements.txt

Thank you All. Finally I rebuilded my app, simplified requirements, exclude alpine and use python 3.7 in my Dockerfile.
I could run app locally, but Docker probably could not find some file from path, or get some other error from app, that is why it stopped just after starting.