The short answer is Google is your friend. The problem is knowing what to Google.
The Anvil documentation doesn’t teach you Python, but you can start asking in this forum, especially when you don’t know if there is an Anvil specific answer or not, like in this case. As you learn Python and Anvil, you will learn also how, what and where to ask your questions.
Stackoverflow.com is the best place for generic Python questions. Usually I start writing the question, creating small examples to put in the question to make it easier for whomever is trying to answer, and often this process alone helps me find the answer. Before posting the question I also check the links to similar questions that automatically pop up on the side.
If I need more details after Stackoverflow, I usually jump to the official Python documentation or any other googlable source. I don’t have any must go place.
For example, after getting an answer like this I would start googling “python magic methods” and “python args kwargs”. Try and you will find tons of yummy stuff about Python.