def cleanup_resources(self, force=False):
<EOL>
Delete all extracted resource files and directories, returning a list
of the file and directory names that could not be successfully removed.
This function does not have any concurrency protection, so it should
generally only be called when the extraction path is a temporary
directory exclusive to a single process.  This method is not
automatically called; you must call it explicitly or register it as an
``atexit`` function if you wish to ensure cleanup of a temporary
directory used for extractions.