Calculate differences between two versions of a directory tree.
Returns a list of zdir_patch_t patches. Either older or newer may
be null, indicating the directory is empty/absent. If alias is set,
generates virtual filename (minus path, plus alias).

def diff(older, newer, alias):
        """
        Calculate differences between two versions of a directory tree.
Returns a list of zdir_patch_t patches. Either older or newer may
be null, indicating the directory is empty/absent. If alias is set,
generates virtual filename (minus path, plus alias).
        """
        return Zlist(lib.zdir_diff(older, newer, alias), True)