10-OOP1.ipynb

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  {
   "cells": [
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Object-Oriented Programming\n",
      "\n",
      "## Basic class operations (\"glorified struct\")"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class MyClass(object):\n",
      "    a = 5\n",
      "    b = 6\n",
      "print MyClass\n",
      "print MyClass.a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "<class '__main__.MyClass'>\n",
        "5\n"
       ]
      }
     ],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "obj = MyClass()\n",
      "print obj.a\n",
      "print obj.b"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "5\n",
        "6\n"
       ]
      }
     ],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "obj.a = 'new value for a'\n",
      "print obj.a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "new value for a\n"
       ]
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print MyClass.a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "5\n"
       ]
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "MyClass.c = 'the c attribute'\n",
      "print MyClass.c"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "the c attribute\n"
       ]
      }
     ],
     "prompt_number": 6
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print obj.c"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "the c attribute\n"
       ]
      }
     ],
     "prompt_number": 7
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Basic methods"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class MyClass(object):\n",
      "    def say(self, something):\n",
      "        print 'MyClass says', something"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 8
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "myobj = MyClass()\n",
      "myobj.say('Hello')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "MyClass says Hello\n"
       ]
      }
     ],
     "prompt_number": 9
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Classes can have a constructor\n",
      "\n",
      "class MyClass(object):\n",
      "    def __init__(self, a, b):\n",
      "        self.a = a\n",
      "        self.b = b\n",
      "        \n",
      "obj = MyClass('avalue', 'bvalue')\n",
      "print obj.a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "avalue\n"
       ]
      }
     ],
     "prompt_number": 11
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Method access and visibility\n",
      "\n",
      "By convention, a single leading underscore indicates that a method or variable is \n",
      "\"protected\" and should not be modified outside the class:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class MyClass(object):\n",
      "    def __init__(self, a, b):\n",
      "        self._a = a\n",
      "        self._b = b\n",
      "    def value(self):\n",
      "        return self._a, self._b\n",
      "    \n",
      "obj = MyClass('avalue', 'bvalue')\n",
      "print obj.value()\n",
      "print obj._a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "('avalue', 'bvalue')\n",
        "avalue\n"
       ]
      }
     ],
     "prompt_number": 12
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "To \"enforce\" private methods / variables, we can use a *double* leading underscore:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class MyClass(object):\n",
      "    def __init__(self, a, b):\n",
      "        self.__a = a\n",
      "        self.__b = b\n",
      "    def value(self):\n",
      "        return self.__a, self.__b\n",
      "        \n",
      "obj = MyClass('avalue', 'bvalue')\n",
      "print obj.value()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "('avalue', 'bvalue')\n"
       ]
      }
     ],
     "prompt_number": 13
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print obj.__a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "ename": "AttributeError",
       "evalue": "'MyClass' object has no attribute '__a'",
       "output_type": "pyerr",
       "traceback": [
        "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[1;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
        "\u001b[1;32m<ipython-input-14-383b7dc3f3c4>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;32mprint\u001b[0m \u001b[0mobj\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0m__a\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
        "\u001b[1;31mAttributeError\u001b[0m: 'MyClass' object has no attribute '__a'"
       ]
      }
     ],
     "prompt_number": 14
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print obj._MyClass__a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "avalue\n"
       ]
      }
     ],
     "prompt_number": 15
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Exercise\n",
      "\n",
      "Write a class to manage a telephone directory. The directory should be \n",
      "stored in a dict as an instance variable. The class should have methods\n",
      "`add_number(name, number)`, `remove_number(name)`, and `lookup_number(name)`."
     ]
    }
   ],
   "metadata": {}
  }
 ]
}