Fix Python – CORS error on same domain?

I’m running into a weird CORS issue right now.
Here’s the error message:
XMLHttpRequest cannot load http://localhost:8666/routeREST/select?q=[…]
Origin http://localhost:8080 is not allowed by Access-Control-Allow-Origin

Two servers:

localhost:8666/routeREST/ : this is a simple Python Bottle server.
localhost:8080/ : Python simpleHTTPserver w….