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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
In Python, "ball_type" is an instance variable not a method. You need to change "ball_type" so that it is set to the "type" parameter.
Perhaps you should start looking at functional programming (especially first-class functions) and why it's important and useful. Almost all the classical (mainstream) languages have adopted and implemented it, so it must have very important uses :P
Also, no, callback hell is another thing, which has already been eliminated with ES6 Promises. It's been pretty much obsolete.