About 9 months into it. I didn't do anything for it to happen—it just happened on its own. I just woke up one day, and sort of "knew" Python—after struggling with basic things for months and giving up.
I had to experiment a lot with different things of course, but that's what makes Python so great, in my opinion—the ease of experimentation with the interpreter and the object model.
This is the most useful part of the Python documentation, in my opinion:
docs.python.org/3/reference/datamodel.html