{
 "metadata": {
  "kernelspec": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "display_name": "IPython (Python 3)",
   "language": "python",
   "name": "python3"
  },
  "name": "",
  "signature": "sha256:2180817d2ec76fd7ba949218adc8f4a2f1718c44eb28cc7c531d499cfb7e90b1"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "Working with the kernel (*Back End*)"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "We can know 'where we are' using the following:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%connect_info"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Now I can open a qtconsole connected to the same kernel:"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "    ipython qtconsole --existing kernel-6ea34ea1-9b11-441d-9f7a-693c1cf71804.json"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "And I can modify what I have in the notebook from the console and viceversa"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "a = 3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "assert a == 3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "-----------------------------"
     ]
    },
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "Creating our own kernels"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "<div class=\"alert-danger\">This recipe was shamelessly stolen from the [excellent cookbook](http://ipython-books.github.io/cookbook/) written by [@cyrillerossant](https://twitter.com/cyrillerossant).</div>"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Let's create a very simple and minimal kernel that will add a modification of the python print function in the notebook."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%writefile printkernel.py\n",
      "\n",
      "from io import StringIO\n",
      "\n",
      "from IPython.kernel.zmq.kernelbase import Kernel\n",
      "from IPython.display import HTML\n",
      "\n",
      "a = '<p style=\"font-size:20px;background-color:black;color:yellow;\">&gt;&gt;&gt;&nbsp;'\n",
      "b = '</p>'\n",
      "\n",
      "class PrintKernel(Kernel):\n",
      "    implementation = 'Print'\n",
      "    implementation_version = '-31.0'\n",
      "    language = 'python'  # will be used for\n",
      "                         # syntax highlighting\n",
      "    language_version = ''\n",
      "    banner = \"Advanced printing in the notebook\"\n",
      "    \n",
      "    def do_execute(self, code, silent,\n",
      "                   store_history=True,\n",
      "                   user_expressions=None,\n",
      "                   allow_stdin=False):\n",
      "\n",
      "        expr = None\n",
      "        try:\n",
      "            expr = code.split('print(')[1].split(')')[0]\n",
      "            out = HTML(a + eval(expr) + b)\n",
      "        except:\n",
      "            pass\n",
      "\n",
      "        if not silent:\n",
      "            if expr:\n",
      "                # We send the standard output to the client.\n",
      "                self.send_response(self.iopub_socket,\n",
      "                    'stream', {\n",
      "                        'name': 'stdout', \n",
      "                        'data': 'Richer print'})\n",
      "\n",
      "                # We prepare the response with our rich data\n",
      "                # (the plot).\n",
      "                content = {\"html\": [out.data],\n",
      "                        \"metadata\": {},\n",
      "                        \"text\": [repr(out)]}\n",
      "\n",
      "                # We send the display_data message with the\n",
      "                # contents.\n",
      "                self.send_response(self.iopub_socket,\n",
      "                    'display_data', content)\n",
      "\n",
      "        # We return the exection results.\n",
      "        return {'status': 'ok',\n",
      "                'execution_count': self.execution_count,\n",
      "                'payload': [],\n",
      "                'user_expressions': {},\n",
      "               }\n",
      "\n",
      "if __name__ == '__main__':\n",
      "    from IPython.kernel.zmq.kernelapp import IPKernelApp\n",
      "    IPKernelApp.launch_instance(kernel_class=PrintKernel)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "My dumb kernel is here. The next step is to indicate to IPython that this new kernel is available. To do this, we need to create a kernel spec kernel.json file and put it in (IPYTHONDIR)/kernels/print/. This file contains the following lines:\n",
      "````\n",
      "{\n",
      " \"argv\": [\"python\", \"-m\",\n",
      "          \"printkernel\", \"-f\",\n",
      "          \"{connection_file}\"],\n",
      " \"display_name\": \"Print\",\n",
      " \"language\": \"python\"\n",
      "}\n",
      "````"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Let's see how the kernel works. Run the following in a console from the same folder where `printkernel.py` and `kernel.json` files are:\n",
      "\n",
      "    ipython notebook --KernelManager.kernel_cmd=\"['python', '-m', 'printkernel', '-f', '{connection_file}']\""
     ]
    },
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "Go deeper"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "https://github.com/takluyver/bash_kernel\n",
      "\n",
      "http://ipython.org/ipython-doc/dev/development/wrapperkernels.html\n",
      "\n",
      "http://nbviewer.ipython.org/github/ipython-books/cookbook-code/blob/master/notebooks/chapter01_basic/06_kernel.ipynb\n",
      "\n",
      "http://ipython.org/ipython-doc/dev/development/messaging.html"
     ]
    }
   ],
   "metadata": {}
  }
 ]
}