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Intro to Python Programming - 3. Basic Input

Hi guys,

          Firstly I would like to thank you all for the giving us the wonderful response for our previous posts! Thank you very much for that. It means a lot to us. :) :D
           
         In my earlier post, I had blogged about Basic Output in Python programming language. I hope you have now understood the concept of printing data onto the standard output device using the print( ) statement.

          In this post, we shall learn how the Python program receives input from the user or standard input device. Once again, as I had mentioned in the earlier post, please be careful regarding the version of python you are using.

          If you are using Python version 2.7, the input function to be used is: raw_input( )

Whereas, if you’re using Python 3.5, then the input function to be used is: input( )

Before we begin into the coding part, let us compare the input operation in Python with the input operation in C as we had did with the print( ) function in our previous post.

C
Python
Uses scanf( ) function.
Uses raw_input( ) or input( ) function.
Makes use of type specifiers like %d, %f etc.
Does not make use of type specifiers.
Can receive multiple inputs using a single scanf( ) function.
Can receive only one input using single raw_input( ) or input( ) function.
e.g. scanf(“%d%f”,&i,&f);
e.g. var = raw_input( )

Now let us learn how to use the raw_input( ) or input( ) funcrions.

The best part about these functions is that, you can write the required message inside these functions; unlike any other programming languages.

For example, if you want to ask the user to enter his/her name, then you can:

name = raw_input( “Enter your name” )  #Python 2.7

name = input( “Enter your name” )         #Python 3.5


Consider a program to input two numbers and display their sum on the screen:

a = int(input( “Enter the first number\t” ))

b = int(input( “Enter the second number\t” ))

sum = a + b

print “The sum is: ”,sum

As you can see, there is a slight change in this program compared to the program to Enter your name. The difference is that, we have encapsulated the input( ) function within the int( ). This is mainly done for type conversion.

The raw_input( ) or input( ) functions executes until the user types a value in the console or shell and Enter or Return is pressed. Later, the input from the user is scanned and parsed as String which is the default parse type for this function.

What I am trying to tell is that, raw_input( ) or input( ) function always considers the input from the user as string, no matter enter an interger number or a single character.

          Hence, when we want the raw_input( ) or input( ) function to know that we want numbers as input and not string, we have to make the type conversion by encapsulating the input( ) function inside the int( ) or float( ).

Here’s a little program to summarize this tutorial:

name = raw_input( "Enter your name\n" )
print "Hello ", name

print "Let us add two numbers and display their sum"

a = int(input( "Enter the first number\t" ))
b = int(input( "Enter the second number\t" ))

sum = a + b

print "The sum is: " ,sum

Output:

Enter your name
User
Hello  User
Let us add two numbers and display their sum
Enter the first number     77
Enter the second number     108
The sum is:  185


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