Configuring nvim-dap-python for live debugging of FastApi application (using Astronvim/Lazy)

[dansereaudd]

I didn't see a Discussions tab for nvim-dap-python repo, so I'm posting here.

I am having a lot of trouble (likely because I am relatively new to neovim, especially debugging setups) setting up nvim-dap-python to allow me to debug a running FastApi server. I've tried leveraging AI tools to help analyze configs/setup (avante-nvim using Claude as an example), but that hasn't been as fruitful as I would have liked.

Setup is as follows:

nvim:

• Astronvim distro, using lazy.nvim as package manager
• Mason-installed debugpy and local (pip) installed debugpy (used for running debugpy server from terminal)
• Default config set for nvim-dap-python (I do not have any lua files that override anything within nvim-dap-python)

python:

• server.py is leveraging FastApi framework, also starts debugpy.listen(), debugpy.wait_for_client(), and uvicorn in the main section; that section looks like this:

if __name__ == "__main__":
    debugpy.log_to("debugpy_logs")
    debugpy.listen(("0.0.0.0", 9096))
    debugpy.wait_for_client()
    print("Debugpy is ready to attach.")

    # Run uvicorn on a separate port
    uvicorn.run(app, host="0.0.0.0", port=9097)

• .vscode/launch.json is used for debugger launch options, the Attach config section looks like this:

{
            "name": "Attach to Local Webserver (9096)",
            "type": "python",
            "request": "attach",
            "connect": {
                "host": "localhost",
                "port": 9096
            },
            "pathMappings": [
                {
                  "localRoot": "${workspaceFolder}",
                   "remoteRoot": "${workspaceFolder}"
                }
            ],
            "justMyCode": false,
            "pythonpath": "python"
        }

From other tests I've done, I know that the debugpy server is starting and that the FastApi server is working normally outside of the debugpy execution. Currently, the debugpy server is started and waits for a client to connect, I go into another terminal window and use keybindings to set a breakpoint and then start DapUI by selecting the Attach to Local Webserver launch option, but I get a message stating "Dap adapter didn't respond..." and then the session terminates moments later.

For the record, I have no issues debugging python files that aren't launched through debugpy. And I've searched for topics related to this issue, but all of them I've seen all mention to use nvim-dap-python to automatically convert type to 'server' when using an 'attach' request, but either that isn't happening for me, or something else is wrong here.

Let me know if any other details or code snippets would be useful here.