{
 "metadata": {
  "name": "Running Code"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "Running Code in the IPython Notebook"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "First and foremost, the IPython Notebook is an interactive environment for writing and running Python code."
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Code cells allow you to enter and run Python code"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Run a code cell using `Shift-Enter` or pressing the \"Play\" button in the toolbar above:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "a = 10"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print(a)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "You can run a cell in place using `Ctrl-Enter`:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "ls"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Managing the IPython Kernel"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Code is run in a separate process called the IPython Kernel.  The Kernel can be interrupted or restarted.  Try running the following cell and then hit the \"Stop\" button in the toolbar above."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import time\n",
      "time.sleep(10)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "If the Kernel dies you will be prompted to restart it. Here we call the low-level system libc.time routine with the wrong argument via\n",
      "ctypes to segfault the Python interpreter:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import sys\n",
      "from ctypes import CDLL\n",
      "# This will crash a Linux or Mac system; equivalent calls can be made on Windows\n",
      "dll = 'dylib' if sys.platform == 'darwin' else 'so.6'\n",
      "libc = CDLL(\"libc.%s\" % dll) \n",
      "libc.time(-1)  # BOOM!!"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Exercise"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Define a variable in a Notebook, then use the \"Kernel:Restart\" menu item to restart the Kernel and verify that the variable has been cleared."
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Working with external code"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "There are a number of ways of getting external code into code cells."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Pasting code with `>>>` prompts works as expected:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      ">>> the_world_is_flat = 1\n",
      ">>> if the_world_is_flat:\n",
      "...     print(\"Be careful not to fall off!\")"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "The `%load` magic lets you load code from URLs or local files:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%load?"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Exercise"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Go to the Matplotlib gallery, view the raw Python code for an example, use `%load` to load it into a cell and then run it.  Make sure you run:\n",
      "\n",
      "    %pylab inline\n",
      "\n",
      "first to enable plotting support."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%load soln/load.py"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Run all"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "It is also possible to run all cells in a Notebook by using the \"Cell\" menu its \"Run All\"."
     ]
    }
   ],
   "metadata": {}
  }
 ]
}