Install argon2 in Docker image (problem with installing gcc)

right now I'm trying to setup argon2 in a docker image. Apparently I have to install gcc before (and I don't just want to install it on my local machine). My Dockerfile looks like this:

FROM python:3.6-alpineRUN mkdir -p /usr/src/appWORKDIR /usr/src/appCOPY requirements.txt /usr/src/app/RUN apt install -y gcc && \pip3 install --no-cache-dir -r requirements.txtCOPY . /usr/src/appEXPOSE 8080ENTRYPOINT ["python3"]CMD ["argon.py"]

and my requirements.txt look like this:

flaskflask_restfulconnexion == 2.2.0python_dateutil == 2.6.0setuptools >= 21.0.0swagger-ui-bundleargon2-cffi

When I try to build my docker container like this I get an error: "/bin/sh: apt: not found"

I'm trying this on ubuntu server 18.04 if this is relevant.