Behaviour of os.path.join

[Beverly Pope]

I wasn’t going to say anything because I haven’t used MS Windows for years.  The OP wants to add a path separator at the end of a path.  Why the OP wants to do that doesn’t concern me.

OTOH, as others have already mentioned, the documentation explicitly says, "If a component is an absolute path, all previous components are thrown away and joining continues from the absolute path component.”  While I may not understand WHY anyone would want that to occur, this was the way it was designed; it is not a bug.

The documentation also says, “The return value is the concatenation of path and any members of *paths with exactly one directory separator (os.sep) following each non-empty part except the last, meaning that the result will only end in a separator if the last part is empty.”  So, the module does allow one to add a path separator at the end of the path by simply adding an empty string as the last part of the path.  The following is on macOS (I don’t have a MS Windows machine):

>>> import os.path
>>> os.path.join('/Users/myID/a', 'b','c')
'/Users/myID/a/b/c'
>>> os.path.join('/Users/myID/a', 'b','c', '')
'/Users/myID/a/b/c/‘

So, it does work as advertised on Python 3.8 and all the OP should need to do is add that empty string to get the OP’s desired result.

Bev in TX