How to keep a docker container run for ever

I created a Dockerfile which sets up python environment so that when people run the image in their host, they can run my python file without installing multiple python packages themselves.

The problem is after I build and run the image, the container stopped immediately (because it completed).

How can I keep the container running forever? My understanding is after people pull and run my image, they can start to run python file by running “python file.python”.

my Dockerfile looks like this (may not be correct. I am still learning):

FROM python:3-alpine
ADD . /app
RUN pip install configparser

Source: StackOverflow