> If you want shared structure of lists in Python, use `itertools.chain`.

That would involve zero shared structure. itertools.chain is just an iterator that iterates one iterable and then, instead of declaring that it's done, goes on to iterate another one.

Shared structure between lists means that two lists refer to some of the same regions of memory.

And multiple `itertools.chain` instances pointing to the same list chunk(s) also use sharing.

OK, that is true, but that approach would have the significant downside that you can't pass over a list more than once.