>Python, as befits Python, has default behavior for instances that I believe is "is" equivalency

Python dicts consider two keys the same if they have the same hash value and are "=="-equal. So __eq__ and __hash__ are the dunder methods to finagle. Python's sets are the same way.

A useful example is with the pathlib library.

    from pathlib import Path
    p = Path('a.txt')
    q = Path('a.txt').absolute()
    p is q # False
    {p, q} # Only one element

"q" carries some different info than "p", but it refers to the same file location. So not considering them distinct values is a good decision for this package.