It's broken just as os.path is. Python doesn't work well with file names in principle: it wants everything to be Unicode. That works for many, but if you want reliable code... you just have to throw all of that away.

Also, in case of pathlib, it adds no value on top of os.path of which it is a wrapper. Instead, it made the original library it wraps worse, because now os.path also needs to know about pathlib to be able to handle path fragments represented as pathlib instances.

All in all, it offers very little utility (a handful of shortcuts) vs increasing the size and memory footprint of "standard" library, complicating dispatch and therefore debugging... it's a bad trade.

Just not to get you confused. It's not an awful trade. It's not like the sky will fall down on you if you use it. It's just mostly worthless, with negligible downsides.