Questions on linked lists

[Kevin Reeder]

The tutorial I'm working through has a section on Linked Lists that
has left me puzzled. I believe I got the basic concept of nodes, embedded
references, and cargo, but when the discussion turned to wrappers,
helpers, preconditions and invariants, I started taking on water. Can anyone
here point me to documentation with a good explanation of this
subject esp in the context of Python?

Kevin