How to fix hot-reload problem on a Flask application inside Docker?

I want my flask application to run with hot reload inside docker container but if I change my app.py flask application to app.run(debug=True,host='0.0.0.0') instead of False, it raises the error:

FileNotFoundError: [Errno 2] No such file or directory: ‘/app/app.py’: ‘/app/app.py’

If I change back to False:

app.run(debug=False,host='0.0.0.0')

it will run, but without hot reload.

My Dockerfile is:

    FROM ubuntu:latest
    RUN apt-get update -y
    RUN apt-get install -y python3-pip python3-dev build-essential locales
    RUN locale-gen en_US.UTF-8  
    ENV LANG en_US.UTF-8  
    ENV LANGUAGE pt_BR:pt:en  
    ENV LC_ALL en_US.UTF-8
    ENV FLASK_ENV="development"
    WORKDIR /app 
    COPY . /app
    VOLUME ["/app"]
    RUN pip3 install -r requirements.txt
    ENTRYPOINT ["python3"]
    CMD ["app.py"]

and I run it using the command:
docker run -p 5000:5000 -v /Users/rodrigodmpa/Documents/IA/web:/app flask-app

Source: StackOverflow