How to include src code into a Python based docker image

Where should I specify Python source in this flake?

I have a project where I do something like:

# ... 
ourCode = builtins.fetchGit (builtins.toString ../.); # (this is in a subdirectory of the main project; YMMV)
# within dockerImage.override
# ...
config.WorkingDir = "${ourCode}";

I did this

          code = pkgs.buildEnv rec {
            name = "code-src";
            paths = [ ./src ];

And included in the contents in Docker image override.