How to efficiently input files with docker

I am starting to get a hand on docker and try to containerized some of the applications I use. Thanks to the tutorial I was able to create docker images and containers but now I am trying to thing about the most efficient and practical ways to do things.

To present my use-case, I have a python code (let’s call it that takes as an input a single .jpg image, does some operations on this image, and then output the processed .jpg image.

Normally I would run it through :

python -i path_of_the_input_image -o path_of_the_output_image

Then, the way I do the connection input/output with my docker is the following. First I create the docker file :

FROM python:3.6.8
COPY . /app
RUN pip install --upgrade pip
RUN pip install -r requirements.txt
CMD python ./ -i ./input_output/input.jpg -o ./input_output/output.jpg

And then after building the image, I run docker run mapping the a local folder with the input_output folder of docker:

docker run -v C:/local_folder/:/app/input_output my_docker_image

This seems to work, but is not really practical, as I have to create locally a specific folder to mount it to the docker container. So here are the questions I am asking myself :

Is there a more practical ways of doings things ? To directly send one single input file and directly receive one single output files from the output of a docker container ?

When I run the docker image, what happens (If I understand correctly) is that it will create a docker container that will run my program once once and then just sits there doing nothing. Even after finishing running it will still be there listed in the command "docker ps -a". Is this behaviour expected ? Is there a way to automatically delete finished container ? Am I using docker run the right way ?

Is there a more practical way of having a container running continuously and on which I can query to run the program on demand with a given input ?

Source: Docker Questions