If you want to run a Dev Container directly using only the Dockerfile, without the need for a devcontainer.json file, here’s how you can do it:

Make sure you have the Dev Containers extension installed in Visual Studio Code.

You already have a Dockerfile in place. For reference, here’s the basic one you provided:

# Dockerfile
FROM python:3.12-slim

WORKDIR /app

COPY . /app

CMD ["python", "app.py"]

Make sure that your Dockerfile is in the root of your project.

Once your Dockerfile is ready, follow these steps:

1. Open your project in VSCode.
2. Press Ctrl+Shift+P and type Dev Containers: Open Folder in Container....
3. Choose the folder containing your Dockerfile.
4. VSCode will automatically detect the Dockerfile and build the development container based on it.

Once the container is built and your environment is set up:

• Open the integrated terminal (Ctrl+ `).
• Run the Python application using:

python app.py

You should see the output Hello, World!.

By doing this, you're directly using the Dockerfile to spin up your development environment inside a container. You get the benefits of containerized development without needing to write a devcontainer.json configuration file. This is useful when you want a minimal setup.