Hello friends and welcome to the tutorial on Input/Output
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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
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%% 1 %% What happens when you do print "x is %d y is %f"%(x)
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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
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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"
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%% 2 %% enter the number 5.6 as input and store it in a variable called c.
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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.
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%% 3 %% What happens when you do not enter anything and hit enter
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::
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.
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%% 4 %% How do you display a prompt and let the user enter input in a new line
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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
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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
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#[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 :
Questions
=========
1. ``a = 2.5``. What is the output of ``print "a is %d"%(a)``
a. a is 2.5
#. a is 2.0
#. 2.0
#. a is 2
Answer: a is 2
2. What does ``print "This is", "a line ", "with spaces"`` print?
a. This is a line with spaces
#. This is a line with spaces
#. This is a line with spaces
#. This is a line with spaces
Answer: This is a line with spaces
3. What does ``print "%2.5f"%(1.2)`` print?
a. 1.2
#. 1.20
#. 1.20000
#. 00001.2
Answer: 1.20000
4. What is the output of the following code::
for i in range(1,10,2):
print i,
Answer::
1 3 5 7 9
5. ``a = 2`` and ``b = 4.5``. What does ``print "a is %d and b is %2.1f"%(b, a)``
print?
a. a is 2 and b is 4.5
#. a is 4 and b is 2
#. a is 4 and b is 2.0
#. a is 4.5 and b is 2
Answer: a is 4 and b is 2.0
6. What is the prompt displayed by ``raw_input("Say something\nType here:")``
Answer::
Say something
Type here:
6. What is the prompt displayed by ``raw_input("value of a is %d\nInput b
value:"a)`` and ``a = 2.5``
Answer::
value of a is 2
Input ba value:
7. ``a = raw_input()`` and user enters ``2.5``. What is the type of a?
a. str
#. int
#. float
#. char
Answer: str
8. ``a = int(raw_input())`` and user enters ``4.5``. What happens?
a. a = 4.5
#. a = 4
#. a = 4.0
#. Error
Answer: Error
9. ``a = raw_input()`` and user enters ``"this is a string"``. What does
``print a`` produce?
a. 'this is a string'
b. 'this is a string"
c. "this is a string"
#. this is a string
Answer: "this is a string"
Problems
========
1. Answer to universe and everything. Keep taking input from user and print it
back until the input is 42.
Answer::
ip = raw_input()
while ip != "42":
print ip
2.