title: ipython --pylab on cygwin: TclError: no display name and no $DISPLAY environment variable
body: <p>I recently installed ipython as per instructions here: <a href="http://ardiyu07.blogspot.com/2012/04/ipython-012-installation-in-cygwin.html" rel="nofollow">http://ardiyu07.blogspot.com/2012/04/ipython-012-installation-in-cygwin.html</a>.</p>
  
  <p>When I run <code>'ipython --pylab'</code> I get the error message below. I have googled around and have found postings about this error but in different context. Mine occurs when I launch ipython with the --pylab argument. I know this has something to do with the matplotlib gui interaction but not sure what exactly. I appreciate the guidance.</p>
  
  <pre><code>$ ipython --pylab
  Python 2.7.3 (default, Dec 18 2012, 13:50:09)
  Type "copyright", "credits" or "license" for more information.
  
  IPython 0.13.1 -- An enhanced Interactive Python.
  ?         -&gt; Introduction and overview of IPython's features.
  %quickref -&gt; Quick reference.
  help      -&gt; Python's own help system.
  object?   -&gt; Details about 'object', use 'object??' for extra details.
  
  Welcome to pylab, a matplotlib-based Python environment [backend: TkAgg].
  For more information, type 'help(pylab)'.
  [TerminalIPythonApp] GUI event loop or pylab initialization failed
  ---------------------------------------------------------------------------
  TclError                                  Traceback (most recent call last)
  /usr/lib/python2.7/site-packages/IPython/core/interactiveshell.pyc in enable_pylab(self, gui, import_all)
     2780         # Now we must activate the gui pylab wants to use, and fix %run to take
     2781         # plot updates into account
  -&gt; 2782         self.enable_gui(gui)
     2783         self.magics_manager.registry['ExecutionMagics'].default_runner = \
     2784         mpl_runner(self.safe_execfile)
  
  /usr/lib/python2.7/site-packages/IPython/lib/inputhook.pyc in enable_gui(gui, app)
      526         e = "Invalid GUI request %r, valid ones are:%s" % (gui, guis.keys())
      527         raise ValueError(e)
  --&gt; 528     return gui_hook(app)
      529
  
  /usr/lib/python2.7/site-packages/IPython/lib/inputhook.pyc in enable_tk(self, app)
      322         if app is None:
      323             import Tkinter
  --&gt; 324             app = Tkinter.Tk()
      325             app.withdraw()
      326             self._apps[GUI_TK] = app
  
  /usr/lib/python2.7/lib-tk/Tkinter.pyc in __init__(self, screenName, baseName, className, useTk, sync, use)
     1683                 baseName = baseName + ext
     1684         interactive = 0
  -&gt; 1685         self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
     1686         if useTk:
     1687             self._loadtk()
  
  TclError: no display name and no $DISPLAY environment variable
  </code></pre>