title: _tkinter.tclerror: bad option set tcl value number must be activate, get, configure
body: <p>Using Tkinter, I have a button that starts an external thread. And a tkinter Textbox that is piped to the external threads stdout and stderr. I got this error only once while executing the external thread:</p>
  
  <pre><code>Exception in Tkinter callback
  Traceback (most recent call last):
    File "C:\Python33\lib\tkinter\__init__.py", line 1475, in __call__
      return self.func(*args)
    File "C:\Python33\lib\tkinter\__init__.py", line 2923, in set
      self.tk.call((self._w, 'set') + args)
  _tkinter.TclError: bad option "set TCL VALUE NUMBER": must be activate, cget, configure, delta, fraction, get, identify, or set
  </code></pre>
  
  <p>Even though it did not occur again, I am curious to find out what caused it. It seems like the error isn't from an external thread but from the main thread that is running the GUI. Could it just be some internal Tkinter error?</p>