Under Windows, pathlib's "absolute" means a fully qualified path as defined in http://msdn.microsoft.com/en-us/library/aa365247%28v=vs.85%29.aspx

>>> PureWindowsPath("c:").is_absolute()
False
>>> PureWindowsPath("/").is_absolute()
False
>>> PureWindowsPath("c:/").is_absolute()
True

The fact that "//server" isn't considered absolute is a bug in pathlib, since "//server/" is:

>>> PureWindowsPath("//foo").is_absolute()
False
>>> PureWindowsPath("//foo/").is_absolute()
True

I agree that it's not really important, since both aren't actual paths (in the sense that they may not point to anything, AFAIK).