Python Input And Output

Python can be used to read and write data. Also it supports reading and writing data to Files.

"print" statement:

"print" statement is used to print the output on the screen.

print statement is used to take string as input and place that string to standard output.

Whatever you want to display on output place that expression inside the inverted commas. The expression whose value is to printed place it without inverted commas.

Syntax:

print "expression"	or	print expression.

eg:

a=10
print "Welcome to the world of Python"
print a

Output:

>>> 
Welcome to the world of Python
10
>>>     

Input from Keyboard:

Python offers two in-built functions for taking input from user. They are:

1) input()

2) raw_input()

1) input() functioninput() function is used to take input from the user. Whatever expression is given by the user, it is evaluated and result is returned back.

Syntax:

input("Expression")

eg:

n=input("Enter your expression ");
print "The evaluated expression is ", n

Output:

>>> 
Enter your expression 10*2
The evaluated expression is  20
>>>    

2) raw_input()raw_input() function is used to take input from the user. It takes the input from the Standard input in the form of a string and reads the data from a line at once.

Syntax:

raw_input(?statement?)

eg:

n=raw_input("Enter your name ");
print "Welcome ", n

Output:

>>> 
Enter your name Rajat
Welcome  Rajat
>>>   

raw_input() function returns a string. Hence in case an expression is to be evaluated, then it has to be type casted to its following data type. Some of the examples are given below:

Program to calculate Simple Interest.

prn=int(raw_input("Enter Principal"))
r=int(raw_input("Enter Rate"))
t=int(raw_input("Enter Time"))
si=(prn*r*t)/100
print "Simple Interest is ",si  

Output:

>>> 
Enter Principal1000
Enter Rate10
Enter Time2
Simple Interest is  200
>>>  

Program to enter details of an user and print them.

name=raw_input("Enter your name ")
math=float(raw_input("Enter your marks in Math"))
physics=float(raw_input("Enter your marks in Physics"))
chemistry=float(raw_input("Enter your marks in Chemistry"))
rollno=int(raw_input("Enter your Roll no"))
print "Welcome ",name
print "Your Roll no is ",rollno
print "Marks in Maths is ",math
print "Marks in Physics is ",physics
print "Marks in Chemistry is ",chemistry
print "Average marks is ",(math+physics+chemistry)/3 

Output:

>>> 
Enter your name rajat
Enter your marks in Math76.8
Enter your marks in Physics71.4
Enter your marks in Chemistry88.4
Enter your Roll no0987645672
Welcome  rajat
Your Roll no is  987645672
Marks in Maths is  76.8
Marks in Physics is  71.4
Marks in Chemistry is  88.4
Average marks is  78.8666666667
>>>

File Handling:

Python provides the facility of working on Files. A File is an external storage on hard disk from where data can be stored and retrieved.

Operations on Files:

1) Opening a File: Before working with Files you have to open the File. To open a File, Python built in function open() is used. It returns an object of File which is used with other functions. Having opened the file now you can perform read, write, etc. operations on the File.

Syntax:

obj=open(filename , mode , buffer) 

here,

filename:It is the name of the file which you want to access.

mode:It specifies the mode in which File is to be opened.There are many types of mode. Mode depends the operation to be performed on File. Default access mode is read.

2) Closing a File:Once you are finished with the operations on File at the end you need to close the file. It is done by the close() method. close() method is used to close a File.

Syntax:

fileobject.close() 

3) Writing to a File:write() method is used to write a string into a file.

Syntax:

fileobject.write(string str)

4) Reading from a File:read() method is used to read data from the File.

Syntax:

fileobject.read(value)

here, value is the number of bytes to be read. In case, no value is given it reads till end of file is reached.

Program to read and write data from a file.

obj=open("abcd.txt","w")
obj.write("Welcome to the world of Python")
obj.close()
obj1=open("abcd.txt","r")
s=obj1.read()
print s
obj1.close()
obj2=open("abcd.txt","r")
s1=obj2.read(20)
print s1
obj2.close()

Output:

>>> 
Welcome to the world of Python
Welcome to the world
>>>

Attributes of File:

There are following File attributes.

Eg:

obj = open("data.txt", "w")
print  obj.name
print  obj.mode
print  obj.closed

Output:

>>> 
data.txt
w
False
>>>

Modes of File:

There are different modes of file in which it can be opened. They are mentioned in the following table.

A File can be opened in two modes:

1) Text Mode.

2) Binary Mode.

Methods:

There are many methods related to File Handling. They are given in the following table:

There is a module "os" defined in Python that provides various functions which are used to perform various operations on Files. To use these functions 'os' needs to be imported.

1) rename():

Syntax:

os.rename(existing_file_name, new_file_name)

eg:

import os
os.rename('mno.txt','pqr.txt')

2) remove():

Syntax:

os.remove(file_name)

eg:

import os
os.remove('mno.txt')

3) mkdir()

Syntax:

eg:

import os
os.mkdir("new")

4) chdir()

Syntax:

eg:

import os
os.chdir("new")

5) getcwd()

Syntax:

eg:

import os
print os.getcwd()

6) rmdir()

Syntax:

eg:

import os
os.rmdir("new")

NOTE: In order to delete a directory, it should be empty. In case directory is not empty first delete the files.