.. Objectives .. ---------- .. #. How to print some value .. #. How to print using modifiers .. #. How to take input from user .. #. How to display a prompt to the user before taking the input .. Prerequisites .. ------------- .. 1. Loops .. Author : Nishanth Amuluru Internal Reviewer : Puneeth External Reviewer : Language Reviewer : Bhanukiran Checklist OK? : [2010-10-05] Script ------ Hello friends and welcome to this tutorial on Input/Output {{{ Show the slide containing title }}} {{{ Show the slide containing the outline slide }}} Input and Output are used in almost every program we use. In this tutorial, we shall learn how to * Output data * Take input from the user type :: a = "This is a string" a print a ``print a``, obviously, is printing the value of ``a``. As you can see, even when you type just a, the value of a is shown. But there is a difference. .. #[Amit: The next sentence does seem to be clear enough] Typing a shows the value of a while print a prints the string. This difference becomes more evident when we use strings with newlines in them. type :: b = "A line \n New line" b print b As you can see, just typing b shows that b contains a newline character. While typing print b prints the string and hence the newline. Moreover when we type just a, the value a is shown only in interactive mode and does not have any effect on the program while running it as a script. .. #[punch: I think we could show that?] We shall look at different ways of outputting the data. .. #[Amit: C's printf syntax ?? i think its better to elaborate the idea] print statement in python supports string formatting. Various arguments can be passed to print using modifiers. type :: x = 1.5 y = 2 z = "zed" print "x is %2.1f y is %d z is %s"%(x,y) As you can see, the values of x and y are substituted in place of ``%2.1f`` and ``%d`` {{{ Pause here and try out the following exercises }}} %% 1 %% What happens when you do ``print "x is %d y is %f" %(x, y)`` {{{ continue from paused state }}} We see that the ``int`` value of x and ``float`` value of y are printed corresponding to the modifiers used in the print statement. We can also see that ``print`` statement prints a new line character at the end of the line, everytime it is called. This can be suppressed by using a "," at the end ``print`` statement. Let us see this by typing out following code on an editor as print_example.py {{{ open an editor }}} type :: print "Hello" print "World" print "Hello", print "World" Now we run the script using %run /home/fossee/print_example.py As we can see, the print statement when used with comma in the end, prints a space instead of a new line. Now we shall look at taking input from the user. We will use the ~~raw_input~~ for this. type :: ip = raw_input() The cursor is blinking indicating that it is waiting for input type :: an input and hit enter. Now let us see what is the value of ip by typing. :: ip We can see that it contains the string "an input" {{{ Pause here and try out the following exercises }}} %% 2 %% enter the number 5.6 as input and store it in a variable called c. {{{ continue from paused state }}} We have to use the raw_input command with variable c. type :: c = raw_input() 5.6 c Now let us see the type of c. :: type(c) We see that c is a string. This implies that anything you enter as input, will be taken as a string no matter what you enter. {{{ Pause here and try out the following exercises }}} %% 3 %% What happens when you do not enter anything and hit enter {{{ continue from paused state }}} :: d = raw_input() d We see that when nothing is entered, an empty string is considered as input. raw_input also can display a prompt to assist the user. :: name = raw_input("Please enter your name: ") prints the string given as argument and then waits for the user input. {{{ Pause here and try out the following exercises }}} %% 4 %% How do you display a prompt and let the user enter input in next line {{{ continue from paused state }}} .. #[Puneeth: We didn't talk of new-line character till now, did we?] .. #[Puneeth: non-programmers might not know?] .. #[Amit: Well there is a discussion earlier about new lines, I think its good .. as a slight trick question. But may be next line is a more easier lexicon] The trick is to include a newline character at the end of the prompt string. :: ip = raw_input("Please enter a number in the next line\n> ") prints the newline character and hence the user enters input in the next line {{{ Show summary slide }}} This brings us to the end of the tutorial. In this totorial we have learnt * How to print some value * How to print using modifiers * How to take input from user * How to display a prompt to the user before taking the input {{{ Show the "sponsored by FOSSEE" slide }}} This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India Hope you have enjoyed and found it useful. Thank You.