Can't quit PyQt5 application with embedded iPython Qtconsole

Question

I'm trying to embed an iPython Qtconsole into a PyQt5 app. The embedded console works fine, but when I try to exit the app (either by clicking 'Quit', using Cmd-Q) the Python process hangs and I have to force quit to dismiss the spinning beachball of death. This is on OS X 10.10.2, Python 2.7.9, iPython 3.0.0, and PyQt5 5.3.1. Any thoughts on how to quit properly?

Minimal example, adapted from the iPython examples:

#!/usr/bin/env python
from PyQt5 import Qt

from internal_ipkernel import InternalIPKernel

class SimpleWindow(Qt.QWidget, InternalIPKernel):

    def __init__(self, app):
        Qt.QWidget.__init__(self)
        self.app = app
        self.add_widgets()
        self.init_ipkernel('qt')

    def add_widgets(self):
        self.setGeometry(300, 300, 400, 70)
        self.setWindowTitle('IPython in your app')

        # Add simple buttons:
        self.console = Qt.QPushButton('Qt Console', self)
        self.console.setGeometry(10, 10, 100, 35)
        self.console.clicked.connect(self.new_qt_console)

        self.namespace = Qt.QPushButton('Namespace', self)
        self.namespace.setGeometry(120, 10, 100, 35)
        self.namespace.clicked.connect(self.print_namespace)

        self.count_button = Qt.QPushButton('Count++', self)
        self.count_button.setGeometry(230, 10, 80, 35)
        self.count_button.clicked.connect(self.count)

        # Quit and cleanup
        self.quit_button = Qt.QPushButton('Quit', self)
        self.quit_button.setGeometry(320, 10, 60, 35)
        self.quit_button.clicked.connect(self.app.quit)

        self.app.lastWindowClosed.connect(self.app.quit)

        self.app.aboutToQuit.connect(self.cleanup_consoles)

if __name__ == "__main__":
    app = Qt.QApplication([]) 
    # Create our window
    win = SimpleWindow(app)
    win.show()

    # Very important, IPython-specific step: this gets GUI event loop
    # integration going, and it replaces calling app.exec_()
    win.ipkernel.start()

internal_ipkernel.py:

import sys

from IPython.lib.kernel import connect_qtconsole
from IPython.kernel.zmq.kernelapp import IPKernelApp

def mpl_kernel(gui):
    """Launch and return an IPython kernel with matplotlib support for the desired gui
    """
    kernel = IPKernelApp.instance()
    kernel.initialize(['python', '--matplotlib=%s' % gui,
                       #'--log-level=10'
                       ])
    return kernel


class InternalIPKernel(object):

    def init_ipkernel(self, backend):
        # Start IPython kernel with GUI event loop and mpl support
        self.ipkernel = mpl_kernel(backend)
        # To create and track active qt consoles
        self.consoles = []

        # This application will also act on the shell user namespace
        self.namespace = self.ipkernel.shell.user_ns

        # Example: a variable that will be seen by the user in the shell, and
        # that the GUI modifies (the 'Counter++' button increments it):
        self.namespace['app_counter'] = 0
        #self.namespace['ipkernel'] = self.ipkernel  # dbg

    def print_namespace(self, evt=None):
        print("\n***Variables in User namespace***")
        for k, v in self.namespace.items():
            if not k.startswith('_'):
                print('%s -> %r' % (k, v))
        sys.stdout.flush()

    def new_qt_console(self, evt=None):
        """start a new qtconsole connected to our kernel"""
        return connect_qtconsole(self.ipkernel.connection_file, profile=self.ipkernel.profile)

    def count(self, evt=None):
        self.namespace['app_counter'] += 1

    def cleanup_consoles(self, evt=None):
        for c in self.consoles:
            c.kill()

Answer 1

You have to use a Kernel Manager, like this: Embedding IPython Qt console in a PyQt application

Here is an working example for PyQt5:

import os
os.environ['QT_API'] = 'pyqt5'

from PyQt5 import QtWidgets
from PyQt5 import QtGui
# ipython won't work if this is not correctly installed. And the error message will be misleading
from PyQt5 import QtSvg 

# Import the console machinery from ipython
from IPython.qt.console.rich_ipython_widget import RichIPythonWidget
from IPython.qt.inprocess import QtInProcessKernelManager


def get_app_qt5(*args, **kwargs):
    """Create a new qt5 app or return an existing one."""
    app = QtWidgets.QApplication.instance()
    if app is None:
        if not args:
            args = ([''],)
        app = QtWidgets.QApplication(*args, **kwargs)
    return app

class QIPythonWidget(RichIPythonWidget):
    """ Convenience class for a live IPython console widget. We can replace the standard banner using the customBanner argument"""
    def __init__(self,customBanner=None,*args,**kwargs):
        super(QIPythonWidget, self).__init__(*args,**kwargs)
        if customBanner!=None: self.banner=customBanner
        self.kernel_manager = kernel_manager = QtInProcessKernelManager()
        kernel_manager.start_kernel()
        kernel_manager.kernel.gui = 'qt'
        self.kernel_client = kernel_client = self._kernel_manager.client()
        kernel_client.start_channels()

        def stop():
            kernel_client.stop_channels()
            kernel_manager.shutdown_kernel()
            get_app_qt5().exit()            
        self.exit_requested.connect(stop)

    def pushVariables(self,variableDict):
        """ Given a dictionary containing name / value pairs, push those variables to the IPython console widget """
        self.kernel_manager.kernel.shell.push(variableDict)
    def clearTerminal(self):
        """ Clears the terminal """
        self._control.clear()    
    def printText(self,text):
        """ Prints some plain text to the console """
        self._append_plain_text(text)        
    def executeCommand(self,command):
        """ Execute a command in the frame of the console widget """
        self._execute(command,False)


class ExampleWidget(QtWidgets.QMainWindow):
    """ Main GUI Window including a button and IPython Console widget inside vertical layout """
    def __init__(self, parent=None):
        super(ExampleWidget, self).__init__(parent)
        self.setWindowTitle('iPython in PyQt5 app example')
        self.mainWidget = QtWidgets.QWidget(self)
        self.setCentralWidget(self.mainWidget)
        layout = QtWidgets.QVBoxLayout(self.mainWidget)
        self.button = QtWidgets.QPushButton('Another widget')
        ipyConsole = QIPythonWidget(customBanner="Welcome to the embedded ipython console\n")
        layout.addWidget(self.button)
        layout.addWidget(ipyConsole)        
        # This allows the variable foo and method print_process_id to be accessed from the ipython console
        ipyConsole.pushVariables({"foo":43,"print_process_id":print_process_id})
        ipyConsole.printText("The variable 'foo' and the method 'print_process_id()' are available. Use the 'whos' command for information.\n\nTo push variables run this before starting the UI:\n ipyConsole.pushVariables({\"foo\":43,\"print_process_id\":print_process_id})")
        self.setGeometry(300, 300, 800, 600)

def print_process_id():
    print('Process ID is:', os.getpid())

def main():
    app  = get_app_qt5()
    widget = ExampleWidget()
    widget.show()
    app.exec_()

if __name__ == '__main__':
    main()