It would raise ValueError("Paths don't have the same drive") if the paths on different drivers, which is not documented.
os.path.commonpath raises ValueError when the *paths* are in different drivers, but it is not documented.
Update the document according @Windsooon 's suggestion.
It actually raise ValueError according line 355 of [test of path](https://github.com/python/cpython/blob/master/Lib/test/test_ntpath.py)
https://bugs.python.org/issue6689
.. function:: commonpath(paths)
Return the longest common sub-path of each pathname in the sequence
- *paths*. Raise :exc:`ValueError` if *paths* contains both absolute and relative
- pathnames, or if *paths* is empty. Unlike :func:`commonprefix`, this
- returns a valid path.
+ *paths*. Raise :exc:`ValueError` if *paths* contain both absolute
+ and relative pathnames, the *paths* are on the different drives or
+ if *paths* is empty. Unlike :func:`commonprefix`, this returns a
+ valid path.
.. availability:: Unix, Windows.