Ben, I think it's worth calling out what the rules are around symlinks. I'm
guessing the info that is initially present is a subset of lstat(), so if
that indicates it's a symlink, is_dir() and is_file() will need a stat()
call, *unless* follow_symlinks is False.

Another question: for symlinks, there are two different possible stat
results: one for stat() and one for lstat(). Are these both cached
separately? Or is only one of them? (Experimentally, they are either both
cached or the cache remembers the follow_symlinks flag and re-fetches the
other result.)

Related, "this method always requires a system call", that remark seems to
disregard the cache.

I'd be happy to review a doc update patch if you make one.