winfo_exists

[Dada]

I want to know, whether a window is already open or not. Following a
peace of the code.
-----
...
class Auswahlmenue:
	def __init__(AM):

		AM.Fenster = Toplevel()
	...
	AM.Fenster.destroy(); Startsortierung()
#-------------------------
class Startsortierung:
	def __init__(SS):
		#-------------------------
		def Abbruch(xxx):
			SS.Fenster_2.destroy()
#!! Abfragen, ob bereits ein Auswahlmenü geöffnet ist!
			if not Auswahlmenue.Fenster.winfo_exists():
				Auswahlmenue()
		#-------------------------
		def Auswahl(xxx):
			Auswahlmenue()
		#-------------------------
		def weiter(xxx):
			SS.Fenster_2.destroy()
		#-------------------------
		SS.Fenster_2 = Toplevel()
		Label(SS.Fenster_2, text= u'... ...').pack()
		SF = Button(SS.Fenster_2, text= u'abbrechen', underline= 0)
		SF.pack(side= u'left')
		SS.Fenster_2.bind(sequence= '<KeyPress-a>', func= Abbruch)
		SF = Button(SS.Fenster_2, text= u'Auswahlmenü', underline= 0)
		SF.pack(side= u'left')
		SS.Fenster_2.bind(sequence= '<KeyPress-A>', func= Auswahl)
		SF = Button(SS.Fenster_2, text= u'weiter', underline= 0)
		SF.pack(side= u'right')
		SS.Fenster_2.bind(sequence= '<KeyPress-w>', func= weiter)
		TkFenster.wait_window(SS.Fenster_2)
----
The main programm calls the class Auswahlmenue. In this class the user
can choose Startsortierung. In this class the user may (after a
prozess) go back to Auswahlmenue without destroying the
Startsortierung-window (SS.Fenster_2), because he needs the information
shown there. Or he may go back immeaditely  to Auswahlmenue via Abbruch
(destroying SS.Fenster_2 and opening AM.Fenster). In the first way the
user later will close the SS.Fenster_2-window - but how do I get the
information, the AM.Fenster is already open or not? I do not want have
two AM.Fenster open.
I hoped toget this via winfo_exists, but there´s a mistake in the
if-row.
Indeed I could do it with a global flag, but is there a possibility to
do it with winfo_exists()?

Thanks for help
Dada