Implement a simple doubly-linked list class
Implement a simple doubly-linked list class

Implement a doubly-linked list class, LList. Values are stored in LLNode
objects, along with pointers to the previous and next LLNode. As with SList,
the list should only be manipulated via the provided methods, rather than by
directly editing pointers, since the length is cached.

johnwilmes/py-data-structures