# HG changeset patch # User nishanth # Date 1284567048 -19800 # Node ID 05a7b05061341367242fe890094f975647df9485 # Parent bc023595e167fa00541a45d13df81f6b22e608b0 initial commit for input_output diff -r bc023595e167 -r 05a7b0506134 input_output.rst --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/input_output.rst Wed Sep 15 21:40:48 2010 +0530 @@ -0,0 +1,182 @@ +Hello friends and welcome to the 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 + + * Outputting data + * Taking input from the user + +type +:: + + a = "This is a string" + a + print a + +print a prints the value of a which is obvious. +As you can see, even when you type just a, the value of a is shown. +But there is a difference. + +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. + +We shall look at different ways of outputting the data. + +print statement also accepts the syntax of C's printf statement. +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) + +{{{ 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 +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 a new line + +{{{ continue from paused state }}} + +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 new line + +{{{ Show summary slide }}} + +This brings us to the end of the tutorial. +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 }}} + +#[Nishanth]: Will add this line after all of us fix on one. +This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India + +Hope you have enjoyed and found it useful. +Thankyou + +.. Author : Nishanth + Internal Reviewer 1 : + Internal Reviewer 2 : + External Reviewer :