superpants

host.docker.internal

https://stackoverflow.com/questions/31324981/how-to-access-host-port-from-docker-container

A plug for the pro Kubernetes crowd:

I run microk8s on a 3 node cluster, using FluxCD to deploy and manage my services. I also work with Kubernetes at work, so I'm very familiar with the concepts. But I will never use anything else.

If you want maximum control and flexibility, learn Kubernetes. For a lot of people (myself included) it's overkill, but IMO it's the best.

My main gripe with docker-compose, which is what I used to use, is that service changes require access to the machine. I have to run commands on the host to alter services. With Kubernetes, and more precisely a GitOps model, you can just make a commit to a git repo and it will roll out.

Sorry, I misread your compose file. It should be the name of the PG container, so db:5432

The python container should connect on postgres:5432 not localhost. To the web container, localhost is itself, not the physical host running docker