So there are a number of issues here. Your Dockerfile does not show how you are building and running the application, if there is a multistage pipeline etc. Those would be helpful to see.
Second - there is no world in which you should need Python 2.7 - security updates for it were stopped 4 years ago and it is not maintained or supported. You should not be using it.
Next - why are you manually installing Swift instead of just using a prebuilt Docker image?
Finally Ubuntu 18.04 is EOL as well and is no longer supported. The Swift 5.10 will not run on it