1 .. Objectives

     2 .. ----------

     3 

     4 .. A - Students and teachers from Science and engineering backgrounds

     5    B - 

     6    C - 

     7    D - 

     8 

     9 .. Prerequisites

    10 .. -------------

    11 

    12 ..   1. Loops

    13      

    14 .. Author              : Nishanth Amuluru

    15    Internal Reviewer   : 

    16    External Reviewer   :

    17    Checklist OK?       : <put date stamp here, if OK> [2010-10-05]

    18 

    19 Script

    20 ------

    21 

    22 Hello friends and welcome to the tutorial on Input/Output

    23 

    24 {{{ Show the slide containing title }}}

    25 

    26 {{{ Show the slide containing the outline slide }}}

    27 

    28 Input and Output are used in almost every program we use.

    29 In this tutorial, we shall learn

    30 

    31  * Outputting data

    32  * Taking input from the user

    33 

    34 type

    35 ::

    36  

    37     a = "This is a string"

    38     a

    39     print a

    40      

    41 print a prints the value of a which is obvious.

    42 As you can see, even when you type just a, the value of a is shown.

    43 But there is a difference.

    44 

    45 Typing a shows the value of a while print a prints the string. This difference

    46 becomes more evident when we use strings with newlines in them.

    47 type

    48 ::

    49 

    50     b = "A line \n New line"

    51     b

    52     print b

    53 

    54 As you can see, just typing b shows that b contains a newline character.

    55 While typing print b prints the string and hence the newline.

    56 

    57 Moreover when we type just a, the value a is shown only in interactive mode and

    58 does not have any effect on the program while running it as a script.

    59 

    60 We shall look at different ways of outputting the data.

    61 

    62 print statement also accepts the syntax of C's printf statement.

    63 Various arguments can be passed to print using modifiers.

    64 type

    65 ::

    66 

    67     x = 1.5

    68     y = 2

    69     z = "zed"

    70     print "x is %2.1f y is %d z is %s"%(x,y)

    71 

    72 As you can see, the values of x and y are substituted in place of %2.1f and %d

    73 

    74 {{{ Pause here and try out the following exercises }}}

    75 

    76 %% 1 %% What happens when you do print "x is %d y is %f"%(x)

    77 

    78 {{{ continue from paused state }}}

    79 

    80 We see that the int value of x and float value of y are printed corresponding

    81 to the modifiers used in the print statement.

    82 

    83 We can also see that print statement prints a new line character at the end of

    84 line, everytime it is called. This can be suppressed by using a "," at the end

    85 print statement.

    86 

    87 Let us see this by typing out following code on an editor as print_example.py

    88 

    89 {{{ open an editor }}}

    90 type

    91 ::

    92 

    93     print "Hello"

    94     print "World"

    95 

    96     print "Hello",

    97     print "World"

    98 

    99 Now we run the script using %run /home/fossee/print_example.py

   100 

   101 As we can see, the print statement when used with comma in the end, prints a

   102 space instead of a new line.

   103 

   104 Now we shall look at taking input from the user.

   105 We will use the ~~raw_input~~ for this.

   106 type

   107 ::

   108 

   109     ip = raw_input()

   110 

   111 The cursor is blinking indicating that it is waiting for input    

   112 type

   113 ::

   114 

   115     an input

   116 

   117 and hit enter.

   118 Now let us see what is the value of ip by typing.

   119 ::

   120 

   121     ip

   122 

   123 We can see that it contains the string "an input"

   124 

   125 {{{ Pause here and try out the following exercises }}}

   126 

   127 %% 2 %% enter the number 5.6 as input and store it in a variable called c.

   128 

   129 {{{ continue from paused state }}}

   130 

   131 We have to use the raw_input command with variable c.

   132 type

   133 ::

   134 

   135     c = raw_input()

   136     5.6

   137     c

   138 

   139 Now let us see the type of c.

   140 

   141 ::

   142 

   143     type(c)

   144 

   145 We see that c is a string. This implies that anything you enter as input, will

   146 be taken as a string no matter what you enter.

   147 

   148 {{{ Pause here and try out the following exercises }}}

   149 

   150 %% 3 %% What happens when you do not enter anything and hit enter

   151 

   152 {{{ continue from paused state }}}

   153 

   154 ::

   155 

   156     d = raw_input()

   157     <RET>

   158     d

   159 

   160 We see that when nothing is entered, an empty string is considered as input.

   161 

   162 raw_input also can display a prompt to assist the user.

   163 ::

   164 

   165     name = raw_input("Please enter your name: ")

   166 

   167 prints the string given as argument and then waits for the user input.

   168 

   169 {{{ Pause here and try out the following exercises }}}

   170 

   171 %% 4 %% How do you display a prompt and let the user enter input in a new line

   172 

   173 {{{ continue from paused state }}}

   174 

   175 The trick is to include a newline character at the end of the prompt string.

   176 ::

   177 

   178     ip = raw_input("Please enter a number in the next line\n> ")

   179 

   180 prints the newline character and hence the user enters input in the new line

   181 

   182 {{{ Show summary slide }}}

   183 

   184 This brings us to the end of the tutorial.

   185 we have learnt

   186 

   187  * How to print some value

   188  * How to print using modifiers

   189  * How to take input from user

   190  * How to display a prompt to the user before taking the input

   191 

   192 {{{ Show the "sponsored by FOSSEE" slide }}}

   193 

   194 #[Nishanth]: Will add this line after all of us fix on one.

   195 This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India

   196 

   197 Hope you have enjoyed and found it useful.

   198 Thankyou

   199