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.. 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? : <put date stamp here, if 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()
<RET>
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.
|
