Revert "add shim for external/qt_for_kernel.py"

This reverts commit 91d98a491ab3b4452d4adea58691884093f5df3e.

IPython/lib/qt_for_kernel.py

@@ -1,86 +1,85 b''
 """ Import Qt in a manner suitable for an IPython kernel.
 
 This is the import used for the `gui=qt` or `matplotlib=qt` initialization.
 
 Import Priority:
 
-if Qt has been imported anywhere else:
+if Qt4 has been imported anywhere else:
    use that
 
 if matplotlib has been imported and doesn't support v2 (<= 1.0.1):
     use PyQt4 @v1
 
-Next, ask QT_API env variable
+Next, ask ETS' QT_API env variable
 
 if QT_API not set:
     ask matplotlib via rcParams['backend.qt4']
     if it said PyQt:
         use PyQt4 @v1
     elif it said PySide:
         use PySide
 
     else: (matplotlib said nothing)
         # this is the default path - nobody told us anything
         try:
             PyQt @v1
         except:
             fallback on PySide
 else:
-    use what QT_API says
+    use PyQt @v2 or PySide, depending on QT_API
+    because ETS doesn't work with PyQt @v1.
 
 """
 
 import os
 import sys
 
 from IPython.utils.version import check_version
 from IPython.external.qt_loaders import (load_qt, loaded_api, QT_API_PYSIDE,
                                          QT_API_PYQT, QT_API_PYQT5,
                                          QT_API_PYQTv1, QT_API_PYQT_DEFAULT)
 
 _qt_apis = (QT_API_PYSIDE, QT_API_PYQT, QT_API_PYQT5, QT_API_PYQTv1,
             QT_API_PYQT_DEFAULT)
 
-# Constraints placed on an imported matplotlib
-# TODO: check that this is still consistent with what matplotlib supports,
-# in particular with regard to qt5.
+#Constraints placed on an imported matplotlib
 def matplotlib_options(mpl):
     if mpl is None:
         return
     mpqt = mpl.rcParams.get('backend.qt4', None)
     if mpqt is None:
         return None
     if mpqt.lower() == 'pyside':
         return [QT_API_PYSIDE]
     elif mpqt.lower() == 'pyqt4':
         return [QT_API_PYQT_DEFAULT]
     raise ImportError("unhandled value for backend.qt4 from matplotlib: %r" %
                       mpqt)
 
 def get_options():
     """Return a list of acceptable QT APIs, in decreasing order of
     preference
     """
     #already imported Qt somewhere. Use that
     loaded = loaded_api()
     if loaded is not None:
         return [loaded]
 
     mpl = sys.modules.get('matplotlib', None)
 
     if mpl is not None and not check_version(mpl.__version__, '1.0.2'):
         #1.0.1 only supports PyQt4 v1
         return [QT_API_PYQT_DEFAULT]
 
     qt_api = os.environ.get('QT_API', None)
     if qt_api is None:
         #no ETS variable. Ask mpl, then use either
         return matplotlib_options(mpl) or [QT_API_PYQT_DEFAULT, QT_API_PYSIDE]
     elif qt_api not in _qt_apis:
         raise RuntimeError("Invalid Qt API %r, valid values are: %r" %
                            (qt_api, ', '.join(_qt_apis)))
     else:
         return [qt_api]
 
 api_opts = get_options()
 QtCore, QtGui, QtSvg, QT_API = load_qt(api_opts)