Creating a whole new collection requires some preliminary work. We need to have new algorithms or new internal data structures that offer significant improvements over the built-in collections. It's important to do thorough "Big-O" complexity calculations before designing a new collection. It's also important to use
timeit after an implementation to be sure that the new collection really is an improvement on the built-in class.
We might, for example, want to create a binary search tree structure that will keep the elements in a proper order. As we want this to be a mutable structure, we'll have to perform the following kinds of design activities: