Better error message for unknown input hook

Closes gh-9264

IPython/terminal/pt_inputhooks/__init__.py

@@ -3,14 +3,36 b' import os'
 
 aliases = {
     'qt4': 'qt',
+    'gtk2': 'gtk',
 }
 
+backends = [
+    'qt', 'qt4', 'qt5',
+    'gtk', 'gtk2', 'gtk3',
+    'tk',
+    'wx',
+    'pyglet', 'glut',
+]
+
+class UnknownBackend(KeyError):
+    def __init__(self, name):
+        self.name = name
+
+    def __str__(self):
+        return ("No event loop integration for {!r}. "
+                "Supported event loops are: {}").format(self.name,
+                                    ', '.join(backends))
+
 def get_inputhook_func(gui):
+    if gui not in backends:
+        raise UnknownBackend(gui)
+
     if gui in aliases:
         return get_inputhook_func(aliases[gui])
 
     if gui == 'qt5':
         os.environ['QT_API'] = 'pyqt5'
+        gui = 'qt'
 
     mod = importlib.import_module('IPython.terminal.pt_inputhooks.'+gui)
     return mod.inputhook