{
 "metadata": {
  "name": ""
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "Data I/O, Strings, Dictionary"
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Data I/O"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "In this lecture we shall concentrate on a few more programming tools which might be useful to you later. Let us try to write a simple interpreter today. In the process we shall learn how to write to a file and recall reading from a file."
     ]
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Reading data from the screen"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "This you already do using `input`. Some of you already use `raw_input`, though I did not do it in class. Today I'll formally introduce it. Raw input directly stores the input in a string. You can later process the string in any way you want."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "s = raw_input(\"Input anything : \")\n",
      "print type(s)\n",
      "print s\n",
      "slst = s.split()\n",
      "varname = slst[0]\n",
      "varvalue = float(slst[1])\n",
      "print \"%s has value %f.\" % (varname, varvalue)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "name": "stdout",
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Input anything : a 7\n"
       ]
      },
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "<type 'str'>\n",
        "a 7\n",
        "a has value 7.000000.\n"
       ]
      }
     ],
     "prompt_number": 1
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Command line input"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Sometimes one runs a program where the input to the program is passed via the command line. It is easy to do that in python. For that one has to import a package called `sys`."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "program = \\\n",
      "\"\"\"\n",
      "import sys\n",
      "\n",
      "x = float(sys.argv[1])\n",
      "print x*x\n",
      "\"\"\"\n",
      "\n",
      "progfile = open(\"files/myprogfile.py\", 'w')\n",
      "progfile.write(program)\n",
      "progfile.close()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 2
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "To see that it works, we can print the file"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "progfile = open(\"files/myprogfile.py\", 'r')\n",
      "print progfile.read()\n",
      "progfile.close()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "\n",
        "import sys\n",
        "\n",
        "x = float(sys.argv[1])\n",
        "print x*x\n",
        "\n"
       ]
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "#%run \"files/myprogfile.py\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%run \"files/myprogfile.py\" 1.5"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "2.25\n"
       ]
      }
     ],
     "prompt_number": 5
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Raising errors"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Till now we had been trying to deal with errors using conditionals. However to make the program more readable, one is encouraged to use the `try..except` mechanism provided in python."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "xstr = raw_input(\"Test :\")\n",
      "x = float(xstr)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "name": "stdout",
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Test :34.3\n"
       ]
      }
     ],
     "prompt_number": 6
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def read_number() :\n",
      "    xstr = raw_input(\"Input a number : \")\n",
      "    try :\n",
      "        x = float(xstr)\n",
      "    except ValueError :\n",
      "        raise ValueError('Cannot understand the number %s.' % xstr)\n",
      "    return x"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 7
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "try :\n",
      "    x = read_number()\n",
      "except ValueError, e :\n",
      "    print e\n",
      "    sys.exit(1)\n",
      "        \n",
      "print x*x"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "name": "stdout",
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Input a number : 23.4\n"
       ]
      },
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "547.56\n"
       ]
      }
     ],
     "prompt_number": 8
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Strings"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Some examples of what you can do with strings."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "eg_str = \"This is a sentence. This is another sentence.\\nThis is the second line. This is the second\\nsentence \\\n",
      "which started in the second line but\\nended in the fourth line.\"\n",
      "print eg_str"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "This is a sentence. This is another sentence.\n",
        "This is the second line. This is the second\n",
        "sentence which started in the second line but\n",
        "ended in the fourth line.\n"
       ]
      }
     ],
     "prompt_number": 9
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Substrings\n",
      "eg_str[10:20]"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 10,
       "text": [
        "'sentence. '"
       ]
      }
     ],
     "prompt_number": 10
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print \"The word 'sentence' begins at %d, whereas the word 'sentience' \\\n",
      "starts at %d.\" % (eg_str.find('sentence'), eg_str.find('sentience'))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "The word 'sentence' begins at 10, whereas the word 'sentience' starts at -1.\n"
       ]
      }
     ],
     "prompt_number": 11
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Also in works\n",
      "print ('sentence' in eg_str)\n",
      "print ('starts' in eg_str)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "True\n",
        "False\n"
       ]
      }
     ],
     "prompt_number": 12
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print 'health'.startswith('heal')\n",
      "print 'Python'.endswith('tail')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "True\n",
        "False\n"
       ]
      }
     ],
     "prompt_number": 13
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Replace\n",
      "print eg_str.replace('sentence', 'verdict')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "This is a verdict. This is another verdict.\n",
        "This is the second line. This is the second\n",
        "verdict which started in the second line but\n",
        "ended in the fourth line.\n"
       ]
      }
     ],
     "prompt_number": 14
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print eg_str.split()\n",
      "print eg_str.splitlines()\n",
      "print eg_str.split('a')\n",
      "print eg_str.split('.')\n",
      "for str in eg_str.split('.') :\n",
      "    print str"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "['This', 'is', 'a', 'sentence.', 'This', 'is', 'another', 'sentence.', 'This', 'is', 'the', 'second', 'line.', 'This', 'is', 'the', 'second', 'sentence', 'which', 'started', 'in', 'the', 'second', 'line', 'but', 'ended', 'in', 'the', 'fourth', 'line.']\n",
        "['This is a sentence. This is another sentence.', 'This is the second line. This is the second', 'sentence which started in the second line but', 'ended in the fourth line.']\n",
        "['This is ', ' sentence. This is ', 'nother sentence.\\nThis is the second line. This is the second\\nsentence which st', 'rted in the second line but\\nended in the fourth line.']\n",
        "['This is a sentence', ' This is another sentence', '\\nThis is the second line', ' This is the second\\nsentence which started in the second line but\\nended in the fourth line', '']\n",
        "This is a sentence\n",
        " This is another sentence\n",
        "\n",
        "This is the second line\n",
        " This is the second\n",
        "sentence which started in the second line but\n",
        "ended in the fourth line\n",
        "\n"
       ]
      }
     ],
     "prompt_number": 15
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Checking type of characters in a string\n",
      "print \"'2334' contains only digits : %s\" % '2334'.isdigit()\n",
      "print \"'a123' contains only digits : %s\" % 'a123'.isdigit()\n",
      "print \"Space '    \\n  \\t  ' : %s\" % ' \\n  \\t   '.isspace()\n",
      "print \"'' is a space : %s\" % ''.isspace()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "'2334' contains only digits : True\n",
        "'a123' contains only digits : False\n",
        "Space '    \n",
        "  \t  ' : True\n",
        "'' is a space : False\n"
       ]
      }
     ],
     "prompt_number": 16
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Removing initial and trailing characters\n",
      "print \"+\" + '    This is a   stupid sentence.           \\n'.strip() + \"+\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "+This is a   stupid sentence.+\n"
       ]
      }
     ],
     "prompt_number": 17
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# delimiter.join(list of strings) \n",
      "\n",
      "list_of_sentences = [\"Sky is blue\", \"Classes are boring\", \"Examples are stupid\"]\n",
      "print '. '.join(list_of_sentences) + '.'\n",
      "print \"-\"*50\n",
      "print \".\\n\".join(list_of_sentences) + '.'"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Sky is blue. Classes are boring. Examples are stupid.\n",
        "--------------------------------------------------\n",
        "Sky is blue.\n",
        "Classes are boring.\n",
        "Examples are stupid.\n"
       ]
      }
     ],
     "prompt_number": 18
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Dictionary"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "names = ['Eric', 'Ila', 'Emma', 'John', 'Umesh', 'Asha', 'Akash', 'Kate', 'Uma', 'Sam']\n",
      "scores = [7,8,6,9,10,6,8,7,7,9]\n",
      "\n",
      "score_dict={'Eric' : 7, 'Ila' : 8}\n",
      "print \"Ila scored %d.\" % score_dict['Ila']\n",
      "\n",
      "# One can add.\n",
      "score_dict={}\n",
      "print score_dict\n",
      "\n",
      "for i in range(len(names)) :\n",
      "    score_dict[names[i]] = scores[i]\n",
      "\n",
      "print score_dict"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Ila scored 8.\n",
        "{}\n",
        "{'Emma': 6, 'Akash': 8, 'Sam': 9, 'Ila': 8, 'Asha': 6, 'Kate': 7, 'Umesh': 10, 'Uma': 7, 'John': 9, 'Eric': 7}\n"
       ]
      }
     ],
     "prompt_number": 19
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "for name in score_dict :\n",
      "    print \"%s scored %d\" % (name, score_dict[name])"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Emma scored 6\n",
        "Akash scored 8\n",
        "Sam scored 9\n",
        "Ila scored 8\n",
        "Asha scored 6\n",
        "Kate scored 7\n",
        "Umesh scored 10\n",
        "Uma scored 7\n",
        "John scored 9\n",
        "Eric scored 7\n"
       ]
      }
     ],
     "prompt_number": 20
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def print_score(n) :\n",
      "    if n in score_dict :\n",
      "        print \"%s scored %d.\" %(n, score_dict[n])\n",
      "    else :\n",
      "        print \"%s is not on list.\" % n"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 21
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print_score('Peter')\n",
      "print_score('Asha')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Peter is not on list.\n",
        "Asha scored 6.\n"
       ]
      }
     ],
     "prompt_number": 22
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def tabulate_scores(sd) :\n",
      "    print \"Name     :    Score\"\n",
      "    for name in sorted(sd) :\n",
      "        print \"%5s    :%9d\" % (name, sd[name])\n",
      "    return None"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 23
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "tabulate_scores(score_dict)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Name     :    Score\n",
        "Akash    :        8\n",
        " Asha    :        6\n",
        " Emma    :        6\n",
        " Eric    :        7\n",
        "  Ila    :        8\n",
        " John    :        9\n",
        " Kate    :        7\n",
        "  Sam    :        9\n",
        "  Uma    :        7\n",
        "Umesh    :       10\n"
       ]
      }
     ],
     "prompt_number": 24
    }
   ],
   "metadata": {}
  }
 ]
}