title: tkinter access widget on a different window
body: <p>So I'm fairly new to the tkiner programming and trying my hands at a GUI with more than one window wich should scan Wifi-Hotspots and show me a list of them. I've copied an example from <a href="https://stackoverflow.com/questions/7546050/switch-between-two-frames-in-tkinter">Switch between two frames in tkinter</a> to get the different windows</p>
  
  <p>I have a Main Menu to enable Monitor Mode for the Wifi-Card and to start the scan. I'm calling another frame with a Listbox to show the results.</p>
  
  <p>My problem now is, that the function startScan(self) is called within StartPage, while the Listbox is in PageOne. How can I adress it there and add entrys to it?</p>
  
  <pre><code>class PyWiFi(tk.Tk):
      def __init__(self, *args, **kwargs):
          tk.Tk.__init__(self, *args, **kwargs)
  
          # the container is where we'll stack a bunch of frames
          # on top of each other, then the one we want visible
          # will be raised above the others
          container = tk.Frame(self)
          container.pack(side="top", fill="both", expand=True)
          container.grid_rowconfigure(0, weight=1)
          container.grid_columnconfigure(0, weight=1)
  
          self.frames = {}
          for F in (StartPage, PageOne, PageTwo):
              frame = F(container, self)
              self.frames[F] = frame
              # put all of the pages in the same location; 
              # the one on the top of the stacking order
              # will be the one that is visible.
              frame.grid(row=0, column=0, sticky="nsew")
  
          self.show_frame(StartPage)
  
      def show_frame(self, c):
           '''Show a frame for the given class'''
          frame = self.frames[c]
          frame.tkraise()
  
  class StartPage(tk.Frame):
      def __init__(self, parent, controller):
          tk.Frame.__init__(self, parent) 
          label = tk.Label(self, text="Main Menu", font=TITLE_FONT)
          label.pack(side="top", fill="x", pady=10)
  
          self.var = tk.IntVar()
          monCheck = tk.Checkbutton(self, text="Monitor Mode", variable=self.var, command=self.monSwitch)
  
          scanButton = tk.Button(self, text="Start Scan", command=self.startScan)
          quitButton = tk.Button(self, text="Quit", command=self.master.quit)
          monCheck.pack()
          scanButton.pack()
          quitButton.pack()
  
      def monSwitch(self):
          if(self.var.get()):
               print "Monitor Modus an"
               check_call(["airmon-ng", "start", "wlan0"])
          else:
               print "Monitor Modus aus"
               check_call(["airmon-ng", "stop", "mon0"])
  
      def startScan(self):
          print "Scan gestartet"
          app.show_frame(PageOne)
          output=check_output('iwlist wlan0 scan | grep -E "Channel:|ESSID:"', shell=True)
          netze = output.split()
          print netze
          for i in range(0,(len(netze)/2)-1): 
                string = netze[2*i]+" "+netze[2*i+1]    
                app.frames[PageOne].netzList.insert(END, string)     
  
  
  class PageOne(tk.Frame):
      def __init__(self, parent, controller):
          tk.Frame.__init__(self, parent)     
          label = tk.Label(self, text="Scanergebnisse", font=TITLE_FONT)
          label.pack(side="top", fill="x", pady=10)
          menuButton = tk.Button(self, text="Menu", command=lambda: controller.show_frame(StartPage))
           quitButton = tk.Button(self, text="Quit", command=self.master.quit)
           button = tk.Button(self, text="P2", command=lambda: controller.show_frame(PageTwo))
           netzList = tk.Listbox(self, width=30)
  
          netzList.pack()
          quitButton.pack(side=LEFT)
          menuButton.pack(side=LEFT)
          button.pack(side=LEFT)
  
  
  class PageTwo(tk.Frame):
      def __init__(self, parent, controller):
          tk.Frame.__init__(self, parent)
          label = tk.Label(self, text="This is page 2", font=TITLE_FONT)
          label.pack(side="top", fill="x", pady=10)
          button = tk.Button(self, text="Go to the start page", 
                         command=lambda: controller.show_frame(StartPage))
          button.pack()    
  
  if __name__ == "__main__":
  app = PyWiFi()
  app.resizable(0, 0)
  app.geometry("320x240")
  app.mainloop()
  </code></pre>