[Tkinter] Tkinter GUI works on Windows but not on Ubuntu

[metulburr]

i get this error whenever i switch from one side to the other, regardless of what index im on. On ubuntu 16.04. To me this looks like self.TestX.curselection() returns an empty string instead of an active index of the listbox whenever the other listbox is focused at that time. Or something similar. As seen below i only get the error when i switch to the other column from an already focused and selected index from the other side.

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Output:
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Exception in Tkinter callback
Traceback (most recent call last):
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1540, in __call__
   return self.func(*args)
 File "test.py", line 24, in print1
   print self.Test1.get(self.Test1.curselection())
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2627, in get
   return self.tk.call(self._w, 'get', first)
TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
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Exception in Tkinter callback
Traceback (most recent call last):
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1540, in __call__
   return self.func(*args)
 File "test.py", line 26, in print2
   print self.Test2.get(self.Test2.curselection())
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2627, in get
   return self.tk.call(self._w, 'get', first)
TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
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Output:
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Exception in Tkinter callback
Traceback (most recent call last):
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1540, in __call__
   return self.func(*args)
 File "test.py", line 24, in print1
   print self.Test1.get(self.Test1.curselection())
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2627, in get
   return self.tk.call(self._w, 'get', first)
TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
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Exception in Tkinter callback
Traceback (most recent call last):
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1540, in __call__
   return self.func(*args)
 File "test.py", line 26, in print2
   print self.Test2.get(self.Test2.curselection())
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2627, in get
   return self.tk.call(self._w, 'get', first)
TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
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Exception in Tkinter callback
Traceback (most recent call last):
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1540, in __call__
   return self.func(*args)
 File "test.py", line 24, in print1
   print self.Test1.get(self.Test1.curselection())
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2627, in get
   return self.tk.call(self._w, 'get', first)
TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
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Exception in Tkinter callback
Traceback (most recent call last):
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1540, in __call__
   return self.func(*args)
 File "test.py", line 26, in print2
   print self.Test2.get(self.Test2.curselection())
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2627, in get
   return self.tk.call(self._w, 'get', first)
TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
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Exception in Tkinter callback
Traceback (most recent call last):
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1540, in __call__
   return self.func(*args)
 File "test.py", line 24, in print1
   print self.Test1.get(self.Test1.curselection())
 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2627, in get
   return self.tk.call(self._w, 'get', first)
TclError: bad listbox index "": must be active, anchor, end, @x,y, or a number
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