(Understanding the difference between packages, module hierarchies, and module attributes is table stakes for architecting a large Python package correctly. PIL almost certainly does this to prevent hard-to-debug circular imports elsewhere in their codebase.)
I wish it was clearer sometimes what was a module, and what was an attribute in the core import syntax. `import foo; foo.bar` only breaks if it's a module, and `import foo.bar` only breaks if it's an attribute. If you do `from foo import bar`, the syntax works with both.
If you see `os.path.basename` what could `os.path` be? It would be a module most of the time because it's written with lowercase. `itertools.chain.from_iterable` [1] would be a notable exception.
[1]: https://docs.python.org/3/library/itertools.html#itertools.c...