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   "cells": [
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Classes\n",
      "\n",
      "Write a class called `Point` which stores a point object in $\\mathbb{R}^2$. It should have a method `distance` such that for two points `P` and `Q`, `P.distance(Q)` returns the distance from `P` to `Q`.\n",
      "\n",
      "Write another class `Polygon` which stores an *ordered* list of point objects to represent a polygon. It should have methods `perimeter` and `area` to which returns the perimeter and the area of the polygon. "
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Sample code"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Imports\n",
      "import math"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class Point :\n",
      "    \"\"\"Imitates a point on R^2\n",
      "    Attributes : x, y\n",
      "    Methods : distance(another point)\n",
      "    \"\"\"\n",
      "    \n",
      "    def __init__(self, x, y) :\n",
      "        self.x = x\n",
      "        self.y = y\n",
      "        \n",
      "    def distance(self, p) :\n",
      "        x1 = self.x\n",
      "        y1 = self.y\n",
      "        x2 = p.x\n",
      "        y2 = p.y\n",
      "        \n",
      "        d = math.sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2))\n",
      "        return d\n",
      "    \n",
      "    def __str__(self) :\n",
      "        return \"(%g, %g)\" % (self.x, self.y)\n",
      "        \n",
      "    def __repr__(self) :\n",
      "        return \"Point(%g, %g)\" % (self.x, self.y)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "if __name__ == '__main__' :\n",
      "    p = Point(1, 0)\n",
      "    q = Point(0, 1)\n",
      "    print \"Distance between %s and %s is %g.\" % (p, q, p.distance(q))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Distance between (1, 0) and (0, 1) is 1.41421.\n"
       ]
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class Polygon :\n",
      "    \"\"\"Implements a polygon as a sequence of points.\n",
      "    Attributes : lop : list of points\n",
      "    Methods :\n",
      "        add_point(p) : Adds p to lop.\n",
      "        permimeter : returns the perimeter.\n",
      "    \"\"\"\n",
      "    \n",
      "    def __init__(self, lop) :\n",
      "        self.lop = lop\n",
      "        \n",
      "    def add_point(self, p) :\n",
      "        self.lop.append(p)\n",
      "        \n",
      "    def perimeter(self) :\n",
      "        l = self.lop\n",
      "        per = 0\n",
      "        for i in range(len(l)) :\n",
      "            if i == 0 :\n",
      "                per += l[i].distance(l[-1])\n",
      "            else :\n",
      "                per += l[i].distance(l[i-1])\n",
      "        return per\n",
      "    \n",
      "    def shoelaceterm(self, i) :\n",
      "        l = self.lop\n",
      "        n = len(l)\n",
      "        if i == 0 : \n",
      "            l1x = l[n - 1].x\n",
      "            l1y = l[n - 1].y\n",
      "            l2x = l[0].x\n",
      "            l2y = l[0].y\n",
      "        else :\n",
      "            l1x = l[i - 1].x\n",
      "            l1y = l[i - 1].y\n",
      "            l2x = l[i].x\n",
      "            l2y = l[i].y\n",
      "        return l1x * l2y - l1y * l2x\n",
      "    \n",
      "    def area(self) :\n",
      "        l = self.lop\n",
      "        shoelacesum = 0\n",
      "        for i in range(len(l)) :\n",
      "            shoelacesum += self.shoelaceterm(i)\n",
      "        return 0.5 * shoelacesum\n",
      "    \n",
      "    def __call__(self) :\n",
      "        return (self.perimeter(), self.area())\n",
      "    \n",
      "    def __str__(self) :\n",
      "        lop = self.lop\n",
      "        retstr = \"\"\n",
      "        for p in lop :\n",
      "            retstr += p.__str__() + \" - \"\n",
      "        return retstr\n",
      "    \n",
      "    def __repr__(self) :\n",
      "        lop = self.lop\n",
      "        lstofstr = []\n",
      "        for p in lop :\n",
      "            lstofstr.append(p.__repr__())\n",
      "        retstr = ', '.join(lstofstr)\n",
      "        retstr = \"Polygon(\" + retstr + \")\"\n",
      "        return retstr\n",
      "        "
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "if __name__ == '__main__' :\n",
      "    p = Point(0, 0)\n",
      "    q = Point(1, 0)\n",
      "    r = Point(1, 1)\n",
      "    pol = Polygon([p, q, r])\n",
      "    print pol\n",
      "    print pol.perimeter()\n",
      "    print pol.area()\n",
      "    s = Point(0, 1)\n",
      "    pol.add_point(s)\n",
      "    print pol\n",
      "    print pol.perimeter()\n",
      "    print pol.area()\n",
      "    print pol()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "(0, 0) - (1, 0) - (1, 1) - \n",
        "3.41421356237\n",
        "0.5\n",
        "(0, 0) - (1, 0) - (1, 1) - (0, 1) - \n",
        "4.0\n",
        "1.0\n",
        "(4.0, 1.0)\n"
       ]
      }
     ],
     "prompt_number": 5
    }
   ],
   "metadata": {}
  }
 ]
}