addSeparator_cmd = "import maya.cmds as cmds;import maya.mel as mel;cmds.separator(width=12, height = 35, style='shelf', hr=False, parent=mel.eval(\"tabLayout -q -selectTab $gShelfTopLevel\"))"
win_name = "Addshelf_win"
if cmds.window(win_name, ex = True):
cmds.deleteUI(win_name)
win = cmds.window(win_name)
cmds.columnLayout(adj = True)
cmds.button(l = "Add separator to this active self", command = addSeparator_cmd)
cmds.showWindow(win_name)