error when launching python app

I have built a trivial bot for telegram using python. Now when I run fly launch configuration file fly.toml is created but the field about build configuration is missing. Any attempt to deploy the app results in the following error Error failed to fetch an image or build from source: app does not have a Dockerfile or buildpacks configured. See I don’t get it why I need to create a docker file. When I attempt to build a trivial expressjs app I never create docker file manually and everything works well but this time with python I am struggling to deploy a simple app. Could it be as a result of the app being not a flask/django app but rather a telegram bot?