recitation1.ipynb

{
 "metadata": {
  "name": "recitation1"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# CS1001.py\n",
      "## Extended Introduction to Computer Science with Python, Tel-Aviv University, Spring 2013\n",
      "# Recitation 1 - 28.2-4.3.2013\n",
      "## Last update: 28.2.2013"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Python general comments\n",
      "\n",
      "1. Course site at <http://tau-cs1001-py.wikidot.com>\n",
      "1. Programming language -> Interpreter -> Machine language\n",
      "1. IDLE (editor + interpreter), see site for installation instructions\n",
      "1. Interactive mode vs. Script mode\n",
      "1. Python version 3.2"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* print function - prints a textual representation to the console"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print(\"Hello world!\")"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Hello world!\n"
       ]
      }
     ],
     "prompt_number": 35
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print(\"Hello\", \"world!\")"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Hello world!\n"
       ]
      }
     ],
     "prompt_number": 36
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Variables, types"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* int - integers: ..., -3, -2, -1, 0, 1, 2, 3, ..."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x=5\n",
      "y=-3\n",
      "print(x, type(x))\n",
      "print(y, type(y))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "5 <class 'int'>\n",
        "-3 <class 'int'>\n"
       ]
      }
     ],
     "prompt_number": 37
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x = 5.5\n",
      "print(type(x))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "<class 'float'>\n"
       ]
      }
     ],
     "prompt_number": 38
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* float - floating point numbers, decimal point fractions: -3.2, 1.5, 1e-8, 3.2e5"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x=5.0\n",
      "y=-3.2\n",
      "z=2.2e6\n",
      "print(x, type(x))\n",
      "print(z, type(z))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "5.0 <class 'float'>\n",
        "2200000.0 <class 'float'>\n"
       ]
      }
     ],
     "prompt_number": 39
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* str - character strings, text: \"intro2CS\", 'python'"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x = \"CS1001.py\"\n",
      "y = 'I love python'\n",
      "print(x, type(x))\n",
      "print(y, type(y))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "CS1001.py <class 'str'>\n",
        "I love python <class 'str'>\n"
       ]
      }
     ],
     "prompt_number": 40
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print(type(4), type(4.0), type(\"4\"))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "<class 'int'> <class 'float'> <class 'str'>\n"
       ]
      }
     ],
     "prompt_number": 41
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* bool - boolean values: True and False"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "i_love_python = True\n",
      "python_loves_me = False\n",
      "print(i_love_python, type(i_love_python))\n",
      "print(python_loves_me, type(python_loves_me))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "True <class 'bool'>\n",
        "False <class 'bool'>\n"
       ]
      }
     ],
     "prompt_number": 42
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Operators"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Mathematical operators"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Addition:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "4 + 5"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 45,
       "text": [
        "9"
       ]
      }
     ],
     "prompt_number": 45
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x = 5\n",
      "4 + x"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 46,
       "text": [
        "9"
       ]
      }
     ],
     "prompt_number": 46
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x = 4.0 + 5\n",
      "print(x, type(x))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "9.0 <class 'float'>\n"
       ]
      }
     ],
     "prompt_number": 47
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Subtraction:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x - 3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 48,
       "text": [
        "6.0"
       ]
      }
     ],
     "prompt_number": 48
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Multiplication:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x * 3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 49,
       "text": [
        "27.0"
       ]
      }
     ],
     "prompt_number": 49
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Division - float and integral with / and //:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "10 / 3, 10 // 3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 50,
       "text": [
        "(3.3333333333333335, 3)"
       ]
      }
     ],
     "prompt_number": 50
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Power:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "2 ** 3, 2 ** 3.0, 3 ** 2"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 52,
       "text": [
        "(8, 8.0, 9)"
       ]
      }
     ],
     "prompt_number": 52
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Modolu:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "10 % 3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 53,
       "text": [
        "1"
       ]
      }
     ],
     "prompt_number": 53
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### String operators"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "String concatenation using +:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"Hello\" + \" World\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 55,
       "text": [
        "'Hello World'"
       ]
      }
     ],
     "prompt_number": 55
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "String duplication using *:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"Bye\" * 2"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 58,
       "text": [
        "'ByeBye'"
       ]
      }
     ],
     "prompt_number": 58
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Strings vs. numbers:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "4 + 5"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 59,
       "text": [
        "9"
       ]
      }
     ],
     "prompt_number": 59
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"4\" + \"5\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 60,
       "text": [
        "'45'"
       ]
      }
     ],
     "prompt_number": 60
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"4\" + 5"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "ename": "TypeError",
       "evalue": "Can't convert 'int' object to str implicitly",
       "output_type": "pyerr",
       "traceback": [
        "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
        "\u001b[1;32m<ipython-input-61-f945f8c7e111>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;34m\"4\"\u001b[0m \u001b[1;33m+\u001b[0m \u001b[1;36m5\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
        "\u001b[1;31mTypeError\u001b[0m: Can't convert 'int' object to str implicitly"
       ]
      }
     ],
     "prompt_number": 61
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "4 + \"5\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "ename": "TypeError",
       "evalue": "unsupported operand type(s) for +: 'int' and 'str'",
       "output_type": "pyerr",
       "traceback": [
        "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
        "\u001b[1;32m<ipython-input-62-871c0c3bbca2>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;36m4\u001b[0m \u001b[1;33m+\u001b[0m \u001b[1;34m\"5\"\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
        "\u001b[1;31mTypeError\u001b[0m: unsupported operand type(s) for +: 'int' and 'str'"
       ]
      }
     ],
     "prompt_number": 62
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Comparisons"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "5 < 4"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 63,
       "text": [
        "False"
       ]
      }
     ],
     "prompt_number": 63
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "5 > 4"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 64,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 64
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "5 >= 4"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 65,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 65
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "4 >= 4"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 66,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 66
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "4 <= 3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 73,
       "text": [
        "False"
       ]
      }
     ],
     "prompt_number": 73
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "5 == 4"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 67,
       "text": [
        "False"
       ]
      }
     ],
     "prompt_number": 67
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "5 == 5.0"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 68,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 68
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "5 == \"5\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 69,
       "text": [
        "False"
       ]
      }
     ],
     "prompt_number": 69
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "5 != 4"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 70,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 70
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "2 + 2 == 4"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 71,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 71
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "2 => 3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "ename": "SyntaxError",
       "evalue": "invalid syntax (<ipython-input-72-76c8f045e4cf>, line 1)",
       "output_type": "pyerr",
       "traceback": [
        "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-72-76c8f045e4cf>\"\u001b[1;36m, line \u001b[1;32m1\u001b[0m\n\u001b[1;33m    2 => 3\u001b[0m\n\u001b[1;37m       ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
       ]
      }
     ],
     "prompt_number": 72
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x = 1 / 3 \n",
      "print(x)\n",
      "x == 0.3333333333333333"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "0.3333333333333333\n"
       ]
      },
      {
       "output_type": "pyout",
       "prompt_number": 77,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 77
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Logical operators"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* not:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print(not True)\n",
      "a = 2 == 5\n",
      "print(not a)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "False\n",
        "True\n"
       ]
      }
     ],
     "prompt_number": 83
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* and:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "True and True"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 84,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 84
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "True and False"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 85,
       "text": [
        "False"
       ]
      }
     ],
     "prompt_number": 85
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "False and False"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 86,
       "text": [
        "False"
       ]
      }
     ],
     "prompt_number": 86
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* or:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "True or True"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 87,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 87
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "True or False"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 88,
       "text": [
        "True"
       ]
      }
     ],
     "prompt_number": 88
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Conversions"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Use the functions `int()`, `float()`, and `str()` to convert between types (we will talk about *functions* next time):"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x = \"6\"\n",
      "print(x, type(x))\n",
      "x = int(\"6\")\n",
      "print(x, type(x))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "6 <class 'str'>\n",
        "6 <class 'int'>\n"
       ]
      }
     ],
     "prompt_number": 91
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "float(\"1.25\")"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 92,
       "text": [
        "1.25"
       ]
      }
     ],
     "prompt_number": 92
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "str(4)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 93,
       "text": [
        "'4'"
       ]
      }
     ],
     "prompt_number": 93
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "int(\"a\")"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "ename": "ValueError",
       "evalue": "invalid literal for int() with base 10: 'a'",
       "output_type": "pyerr",
       "traceback": [
        "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
        "\u001b[1;32m<ipython-input-94-91097a4105a2>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"a\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
        "\u001b[1;31mValueError\u001b[0m: invalid literal for int() with base 10: 'a'"
       ]
      }
     ],
     "prompt_number": 94
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "course = \"intro\" + str(2) + \"cs\"\n",
      "print(course)\n",
      "print(\"intro\", 2, \"cs\", sep='')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "intro2cs\n",
        "intro2cs\n"
       ]
      }
     ],
     "prompt_number": 98
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Flow control"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Conditional statements"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "The `if` condition formula - replace conditions and statements with meaningful code:\n",
      "\n",
      "    if *condition*:\n",
      "        *statement*\n",
      "        *statement*\n",
      "        ...\n",
      "    elif *condition*: # 0 or more elif clauses\n",
      "        *statement*\n",
      "        *statement*\n",
      "        ...    \n",
      "    else:             # optional\n",
      "        *statement*\n",
      "        *statement*\n",
      "\n",
      "Example:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "today = \"Monday\"\n",
      "strike = \"N\"\n",
      "my_recitation = \"Monday\"\n",
      "\n",
      "if today == \"Sunday\":\n",
      "    print(\"Shvizut Yom Alef\")\n",
      "    if strike == \"Y\":\n",
      "        print(\"Stay home\")\n",
      "    else:\n",
      "        print(\"Lecture in intro to CS!\")\n",
      "elif today == \"Wednesday\":\n",
      "    print(\"Another lecture in intro to CS!\")\n",
      "elif today == my_recitation:\n",
      "    print(\"Go to recitation!\")\n",
      "elif today == \"Monday\" or today == \"Tuesday\" or today == \"Thursday\" or \\\n",
      "                    today == \"Friday\" or today == \"Saturday\":\n",
      "    print(\"no intro to CS\")\n",
      "else:\n",
      "    print(\"Not a day\")"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Go to recitation!\n"
       ]
      }
     ],
     "prompt_number": 101
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Loops"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* While:"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "    while *condition*:\n",
      "        *statement*\n",
      "        *statement*\n",
      "\n",
      "Example - count how many times 0 appears in an integer number:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "num = 2**100\n",
      "print(num)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "1267650600228229401496703205376\n"
       ]
      }
     ],
     "prompt_number": 102
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "count = 0\n",
      "\n",
      "while num > 0:   #what if we changed to >=0?\n",
      "    if num % 10 == 0:\n",
      "        count = count + 1\n",
      "    num = num // 10\n",
      "\n",
      "print(count)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "6\n"
       ]
      }
     ],
     "prompt_number": 103
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* For:"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "    for *variable* in *iterable*:\n",
      "        *statement*\n",
      "        *statement*\n",
      "\n",
      "Example - solve the same problem with a `str` type instead of `int`:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "num = 2**100\n",
      "count = 0\n",
      "for digit in str(num):\n",
      "    #print(digit, type(digit))\n",
      "    if digit == \"0\":\n",
      "        count = count + 1\n",
      "\n",
      "print(count)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "6\n"
       ]
      }
     ],
     "prompt_number": 105
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Builtin solution:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "num = 2**100\n",
      "count = str.count(str(num), \"0\")\n",
      "\n",
      "print(count)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "6\n"
       ]
      }
     ],
     "prompt_number": 106
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Efficiency"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "We can measure which solution is faster:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%timeit\n",
      "num = 2**100\n",
      "count = 0\n",
      "while num>0:   #what if we changed to >=0?\n",
      "    if num % 10 == 0:\n",
      "        count = count + 1\n",
      "    num = num // 10"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "10000 loops, best of 3: 37.4 us per loop\n"
       ]
      }
     ],
     "prompt_number": 108
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%timeit \n",
      "num = 2**100\n",
      "count = 0\n",
      "for digit in str(num):\n",
      "    if digit == \"0\":\n",
      "        count = count + 1"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "100000 loops, best of 3: 8.76 us per loop\n"
       ]
      }
     ],
     "prompt_number": 109
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%timeit \n",
      "num = 2**100\n",
      "count = str.count(str(num), \"0\")"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "100000 loops, best of 3: 2.82 us per loop\n"
       ]
      }
     ],
     "prompt_number": 110
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "The builtin solution is 4 times faster than the `for` solution which is 3 times faster than the `while` solution."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### Other notes"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* The `while` solution will not work for `num <= 0`\n",
      "* The `while` solution will not work for non-numerals (e.g, `num = \"Cola 0 is awesome!\"`)\n",
      "* The builtin solution is implemented with C and that is why it is faster"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Fin"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "This notebook is part of the [Extended introduction to computer science](http://tau-cs1001-py.wikidot.com/) course at Tel-Aviv University.\n",
      "\n",
      "The notebook was written using Python 3.2 and IPython 0.13.1.\n",
      "\n",
      "The code is available at <https://raw.github.com/yoavram/CS1001.py/master/recitation1.ipynb>.\n",
      "\n",
      "The notebook can be viewed online at <http://nbviewer.ipython.org/urls/raw.github.com/yoavram/CS1001.py/master/recitation1.ipynb>.\n",
      "\n",
      "The notebooks is also available as a PDF at <https://github.com/yoavram/CS1001.py/blob/master/recitation1.pdf?raw=true>.\n",
      "\n",
      "This work is licensed under a [Creative Commons Attribution-ShareAlike 3.0 Unported License](http://creativecommons.org/licenses/by-sa/3.0/)."
     ]
    }
   ],
   "metadata": {}
  }
 ]
}