Building with Python 3.9 (vs default 3.8)

Questions / Help
1

I’m trying to deploy and application that requires Python 3.9.

Because the app is very very simple, I’d rather not get into the custom image/docker configuration.

The auto-generated fly.toml says:

[build]
  builtin = "python"

From: defaultbuiltins.go

I see this defaults to Python image: 3.8-slim-buster

But looks like there may be a way for me to pass a different tag:

Template: `FROM python:{{- .pythonbase }}

What is the syntax to use python:3.9-slim-buster in fly.toml?

I’d expect this to be documented in the build section of the configuration documentation, but builtin is not mentioned there at all.

Thank you,
M

2

After some stabbing in the dark, found this (undocumented) syntax to work:

[build]
  builtin = "python"

[build.settings]
  pythonbase = "3.9-slim-buster"
2 Likes
3

Oh good find. We have some Python work to do, for sure, this is not a great UX.

4

Other than having to guess that parameter, setting up my Python project was a breeze!

Init add Procfile, deploy. Done!

Great experience overall!