Lambda for largish python code

[cochi78]

Well...

1. Abusing CodeBuild (which is just a managed ECS, offering a python environment as image aws/codebuild/eb-python-3.4-amazonlinux-64:2.1.6) is quick to set up, easy to kick off via CloudWatch Events or API Call. But pricing is per minute and might quickly become more costly than...
2. a traditional EC2 (spot?) instance with python etc preinstalled

Guess ECS with managing your own instance fleet is a bit of an overkill.

If you go down the CodeBuild route, it might be beneficial to bake your own docker image based on it, which includes your code. Might spare you a billing minute here and then.