title: tcl_error in Tkinter when launching python IDLE from Cygwin
body: <p>I tried to launch <code>IDLE</code> from cygwin and I got the below error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/usr/bin/idle", line 5, in &lt;module&gt;
      main()
    File "/usr/lib/python2.7/idlelib/PyShell.py", line 1537, in main
      root = Tk(className="Idle")
    File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1764, in __init__
      self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk,         sync, use)
  _tkinter.TclError: no display name and no $DISPLAY environment variable
  </code></pre>
  
  <p>I can launch the <code>IDLE</code> from the <code>idle.bat</code> file as  <code>cygstart idle.bat</code>.</p>
  
  <p>I searched for an explanation of this error and could not find one.  I have also added <code>IDLE</code> as an environmental variable in cygwin.  When I do <code>printenv</code>, it shows up as an environmental variable.  Just in case this was the problem, I tried two environmental variables:</p>
  
  <p><code>idle=C:\Python27\Lib\idlelib\idle.bat</code>
  <code>PATH = cygdrive/c/Python27/Lib/idlelib</code></p>
  
  <p>I also have the cygwin <code>IDLE</code> package installed.</p>
  
  <p><strong>What could be the problem?</strong> </p>