OOP Review

oop_review.ipynb

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     "source": [
      "Agenda\n",
      "---\n",
      "\n",
      "- Recap: Message Passing\n",
      "- Object-Oriented Programming (OOP)\n",
      "- Inheritance\n",
      "- Polymorphism"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Recap: Message-Passing\n",
      "---\n",
      "\n",
      "In message passing, it is the data that is \u201cintelligent\u201d:\n",
      "\n",
      "- They know how to act on themselves\n",
      "- You just \"tell\" the data what you want done\n",
      "- Pass messages to the object"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def make_rect(x,y):\n",
      "    def helper(msg):\n",
      "        if msg == \"get_real\":\n",
      "            return x\n",
      "        elif msg == \"get_imag\":\n",
      "            return y\n",
      "        elif msg == \"angle\":\n",
      "            return math.atan(y/x)\n",
      "        elif msg == \"magnitude\":\n",
      "            return math.sqrt(x*x+y*y)\n",
      "        else:\n",
      "            raise Exception(\"Invalid method!\")\n",
      "    return helper\n",
      "\n",
      "def make_polar(r,a):\n",
      "    def helper(msg):\n",
      "        if msg == \"get_real\":\n",
      "            return r*math.cos(a)\n",
      "        elif msg == \"get_imag\":\n",
      "            return r*math.sin(a)\n",
      "        elif msg == \"angle\":\n",
      "            return a\n",
      "        elif msg == \"magnitude\":\n",
      "            return r\n",
      "        else:\n",
      "            raise Exception(\"Invalid method!\")\n",
      "    return helper"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 9
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "z1 = make_rect(1,1)\n",
      "print(z1(\"get_real\"))\n",
      "print(z1(\"get_imag\"))\n",
      "print(z1(\"angle\"))\n",
      "print(z1(\"magnitude\"))\n",
      "z2 = make_rect(1,0)\n",
      "print(z2(\"get_real\"))\n",
      "print(z2(\"get_imag\"))\n",
      "print(z2(\"angle\"))\n",
      "print(z2(\"magnitude\"))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "1\n",
        "1\n",
        "0.785398163397\n",
        "1.41421356237\n",
        "1\n",
        "0\n",
        "0.0\n",
        "1.0\n"
       ]
      }
     ],
     "prompt_number": 10
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Recap: Message Passing\n",
      "---\n",
      "\n",
      "- Effectively, each data object stores its own lookup table!\n",
      "- Match function to representation:\n",
      "  - Dispatch on Type (if-else)\n",
      "  - Data-Directed Programming (lookup table)\n",
      "  - Message Passing (function in data)"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Object-Oriented Programming\n",
      "---\n",
      "Combines two powerful computational ideas:\n",
      "\n",
      "1. Generic operations (\u201cmessage passing\u201d)\n",
      "2. Object-based abstractions\n",
      "\n",
      "Major concepts:\n",
      "\n",
      "- Classes and instances\n",
      "- Methods and message passing\n",
      "- Inheritance\n",
      "- Polymorphism"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class BankAccount(object):\n",
      "    def __init__(self, initial_balance): # Constructor (recall: data abstraction?)\n",
      "        self.balance = initial_balance\n",
      "\n",
      "    def withdraw(self, amount): # Actions\n",
      "        if self.balance > amount:\n",
      "            self.balance -= amount\n",
      "            return self.balance\n",
      "        else:\n",
      "            return \"Money not enough\"\n",
      "        \n",
      "    def deposit(self, amount):\n",
      "        self.balance += amount\n",
      "        return self.balance\n"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 13
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "The code above defines a **class**, whereas in the example below, we're creating an **instance** (`ben_account`) of the class `BankAccount`"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      ">>> ben_account = BankAccount(100)\n",
      ">>> ben_account.withdraw(40) # 60\n",
      ">>> ben_account.withdraw(200) # \"Money not enough\"\n",
      ">>> ben_account.deposit(20) #80"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 15,
       "text": [
        "80"
       ]
      }
     ],
     "prompt_number": 15
    },
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     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Inheritance\n",
      "---\n",
      "\n",
      "- Objects that exhibit similar functionality should \u201cinherit\u201d from the same base object, called the **superclass**.\n",
      "- An object that inherits from another is called the **subclass**\n",
      "- Superclass vs Subclass\n",
      "  - Subclass specializes the superclass by extending state/behavior\n",
      "- Classes have an \u201cis-a\u201d relationship with their superclasses (establishes a type hierarchy)\n",
      "\n",
      "**Remark**: Attempt and understand Mission 14 to brush up on your understanding!"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Do you notice repeated code?"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class NamedObject(object):\n",
      "   def __init__ (self, name):\n",
      "     self.name = name # repeated\n",
      "\n",
      "\n",
      "class MobileObject(NamedObject):\n",
      "   def __init__ (self, name, location):\n",
      "     self.name = name # repeated\n",
      "     self.location = location"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 17
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "The \u2018super()\u2019 method"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class NamedObject(object):\n",
      "   def __init__(self, name):\n",
      "     self.name = name.lower()\n",
      "\n",
      "\n",
      "class MobileObject(NamedObject):\n",
      "   def __init__(self, name, location):\n",
      "     super().__init__(name)\n",
      "     self.location = location\n"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 18
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Another Example (slides 64 - 72)"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class Speaker(object):\n",
      "    def say(self,stuff):\n",
      "        print(stuff)\n",
      "\n",
      "class Lecturer(Speaker):\n",
      "\tdef lecture(self, stuff):\n",
      "\t\tself.say(stuff) # whatever a speaker is supposed to do\n",
      "\t\tself.say(\"You should be taking notes\") # Extends the behavior of a speaker\n",
      "        \n",
      "class ArrogantLecturer(Lecturer):\n",
      "\tdef __init__(self, favourite_phrase):\n",
      "\t\tself.favourite_phrase = favourite_phrase\n",
      "\n",
      "\tdef say(self, stuff):\n",
      "\t\tsuper().say(stuff + self.favourite_phrase) # what is super() here referring to?"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 27
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "I'll skip through Polymorphism ..."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Multiple Inheritance\n",
      "---"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class Singer(object):\n",
      "\tdef say(self, stuff):\n",
      "\t\tprint(\"tra-la-la -- \" + stuff)\n",
      "\n",
      "\tdef sing(self):\n",
      "\t\tprint(\"tra-la-la\")\n",
      "\n",
      "class SingingArrogantLecturer(ArrogantLecturer, Singer): # what are the superclasses here? 2 of them!\n",
      "\tdef __init__(self, favourite_phrase):\n",
      "\t\tsuper().__init__(favourite_phrase)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 29
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [],
     "language": "python",
     "metadata": {},
     "outputs": []
    }
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