import tkinter

class MyApp(tkinter.Frame):
    def __init__(self, master=None):
        super().__init__(master)
        self.pack(padx=300,pady=200)
        self.createWidgets()
    def createWidgets(self):
        self.nameEntry = tkinter.Entry(self)
        self.nameEntry.pack(side="left")
        self.name = tkinter.StringVar()
        self.name.set("Ihr Name:")
        self.nameEntry["textvariable"]=self.name
        self.ok = tkinter.Button(self)
        self.ok["text"] = "OK"
        self.ok["command"] = self.quit
        self.ok.pack(side="right")
        self.rev = tkinter.Button(self)
        self.rev["text"]="Umdrehen"
        self.rev["command"]=self.onReverse
        self.rev.pack(side="right")
    def onReverse(self):
        self.name.set(self.name.get()[::-1])

root = tkinter.Tk()
app = MyApp(root)
app.mainloop()