I would like to rename the new layer which i just created.
floating_sel = pdb.gimp_selection_float(drawable, 0, 0)
pdb.gimp_floating_sel_to_layer(floating_sel)
pdb.gimp_item_set_name(item, "s")
You've already got the item to pass into pdb.gimp_item_set_name : floating_sel
pdb.gimp_item_set_name(floating_sel, "s")