title: cannot use geometry manager pack inside . which already has slaves managed by grid, although master windows are different
body: <p>I want to use grid to position frames in root, and use pack to position button in first frame. The master window is different, so why do I get this error?</p>
  <pre><code>root = Tk()
  
  frame1 = LabelFrame(root, text=&quot;Frame1&quot;).grid(row=0, column=0)
  frame2 = LabelFrame(root, text=&quot;Frame2&quot;).grid(row=0, column=1)
  
  
  def open_file():
      pass
  
  btn_import_image = Button(frame1, text=&quot;Import&quot;, command=open_file)
  btn_import_image.pack()
  
  
  root.mainloop()
  </code></pre>
  <p>Error:</p>
  <pre><code>_tkinter.TclError: cannot use geometry manager pack inside . which already has slaves managed by grid
  </code></pre>