Create a QApplication for inputhook if one doesn't already exist

Closes gh-9784

IPython/terminal/pt_inputhooks/qt.py

@@ -1,25 +1,30 b''
 import sys
 from IPython.external.qt_for_kernel import QtCore, QtGui
 
+# If we create a QApplication, keep a reference to it so that it doesn't get
+# garbage collected.
+_appref = None
+
 def inputhook(context):
+    global _appref
     app = QtCore.QCoreApplication.instance()
     if not app:
-        return
+        _appref = app = QtGui.QApplication([" "])
     event_loop = QtCore.QEventLoop(app)
 
     if sys.platform == 'win32':
         # The QSocketNotifier method doesn't appear to work on Windows.
         # Use polling instead.
         timer = QtCore.QTimer()
         timer.timeout.connect(event_loop.quit)
         while not context.input_is_ready():
             timer.start(50)  # 50 ms
             event_loop.exec_()
             timer.stop()
     else:
         # On POSIX platforms, we can use a file descriptor to quit the event
         # loop when there is input ready to read.
         notifier = QtCore.QSocketNotifier(context.fileno(), QtCore.QSocketNotifier.Read)
         notifier.setEnabled(True)
         notifier.activated.connect(event_loop.exit)
         event_loop.exec_()