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

     2 

     3 {{{ Show the slide containing title }}}

     4 

     5 {{{ Show the slide containing the outline slide }}}

     6 

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

     8 In this tutorial, we shall learn

     9 

    10  * Outputting data

    11  * Taking input from the user

    12 

    13 type

    14 ::

    15  

    16     a = "This is a string"

    17     a

    18     print a

    19      

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

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

    22 But there is a difference.

    23 

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

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

    26 type

    27 ::

    28 

    29     b = "A line \n New line"

    30     b

    31     print b

    32 

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

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

    35 

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

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

    38 

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

    40 

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

    42 Various arguments can be passed to print using modifiers.

    43 type

    44 ::

    45 

    46     x = 1.5

    47     y = 2

    48     z = "zed"

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

    50 

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

    52 

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

    54 

    55 %% 1 %% What happens when you do print "x is %d y is %f"%(x)

    56 

    57 {{{ continue from paused state }}}

    58 

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

    60 to the modifiers used in the print statement.

    61 

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

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

    64 print statement.

    65 

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

    67 

    68 {{{ open an editor }}}

    69 type

    70 ::

    71 

    72     print "Hello"

    73     print "World"

    74 

    75     print "Hello",

    76     print "World"

    77 

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

    79 

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

    81 space instead of a new line.

    82 

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

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

    85 type

    86 ::

    87 

    88     ip = raw_input()

    89 

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

    91 type

    92 ::

    93 

    94     an input

    95 

    96 and hit enter.

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

    98 ::

    99 

   100     ip

   101 

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

   103 

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

   105 

   106 %% 2 %% enter the number 5.6 as input and store it in a variable called c.

   107 

   108 {{{ continue from paused state }}}

   109 

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

   111 type

   112 ::

   113 

   114     c = raw_input()

   115     5.6

   116     c

   117 

   118 Now let us see the type of c.

   119 

   120 ::

   121 

   122     type(c)

   123 

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

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

   126 

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

   128 

   129 %% 3 %% What happens when you do not enter anything and hit enter

   130 

   131 {{{ continue from paused state }}}

   132 

   133 ::

   134 

   135     d = raw_input()

   136     <RET>

   137     d

   138 

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

   140 

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

   142 ::

   143 

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

   145 

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

   147 

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

   149 

   150 %% 4 %% How do you display a prompt and let the user enter input in a new line

   151 

   152 {{{ continue from paused state }}}

   153 

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

   155 ::

   156 

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

   158 

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

   160 

   161 {{{ Show summary slide }}}

   162 

   163 This brings us to the end of the tutorial.

   164 we have learnt

   165 

   166  * How to print some value

   167  * How to print using modifiers

   168  * How to take input from user

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

   170 

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

   172 

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

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

   175 

   176 Hope you have enjoyed and found it useful.

   177 Thankyou

   178  

   179 .. Author              : Nishanth

   180    Internal Reviewer 1 : 

   181    Internal Reviewer 2 : 

   182    External Reviewer   :