Notes And Questions NCERT Class 12 Computer Science Chapter 3 File handling

Please refer to File handling Class 12 Computer Science Notes and important questions below. The Class 12 Computer Science Chapter wise notes have been prepared based on the latest syllabus issued for the current academic year by CBSE. Students should revise these notes and go through important Class 12 Computer Science examination questions given below to obtain better marks in exams

File handling Class 12 Computer Science Notes and Questions

The below Class 12 File handling notes have been designed by expert Computer Science teachers. These will help you a lot to understand all the important topics given in your NCERT Class 12 Computer Science textbook. Refer to Chapter 3 File handling Notes below which have been designed as per the latest syllabus issued by CBSE and will be very useful for upcoming examinations to help clear your concepts and get better marks in examinations.

Learning Outcomes: Learn file handling in Python.

INTRODUCTION:

File:- A file is a collection of related data stored in computer storage for future data retrieval.
Stream: – It refers to a sequence of bytes.
File handling refres to reading and writing contents from a file.
Data Files:
Data files can be stored in two ways:
1. Text Files: Text files are structured as a sequence of lines, where each line includes a sequence of characters.
2. Binary Files : A binary file is any type of file that is not a text file.

S. No.	Text Files	Binary Files
1.	Stores information in ASCII characters.	Stores information in the same format which the information is held in memory.
2.	Each line of text is terminated with a special character known as EOL (End of Line)	No delimiters are used for a line.
3.	Some internal translations take place when this EOL character is read or written.	No translation occurs in binary files.
4.	Slower than binary files.	Binary files are faster and easier for a program to read and write the text files.

Opening and closing a file:

Opening a file: To work with a file, first of all you have to open the file. To open a file in python, we use open( ) function.
The open( ) function takes two parameters; filename, and mode. open( ) function returns a file object.
Syntax: file_objectname= open(filename, mode)
Example: To open a file for reading it is enough to specify the name of the file: f = open(“book.txt”)
The code above is the same as:
f = open(“book.txt”, “rt”)
Where “r” for read mode, and “t” for text are the default values, you do not need to specify them.

Closing a file:
After performing the operations, the file has to be closed. For this, a close( ) function is used to close a file.
Syntax:
file-objectname.close( )

File Modes:

Text file mode	Binary File Mode	Description
‘r’	‘rb’	Read – Default value. Opens a file for reading, error if the file does not exist.
‘w’	‘wb’	Write – Opens a file for writing, creates the file if it does not exist
‘a’	‘ab’	Append – Opens a file for appending, creates the file if it does not exist
‘r+’	‘rb+’	Read and Write-File must exist, otherwise error is raised.
‘w+’	‘wb+’	Read and Write-File is created if does not exist.
‘a+’	‘ab+’	Read and write-Append new data
‘x’	‘xb’	Create – Creates the specified file, returns an error if the file exists

In addition you can specify if the file should be handled as binary or text mode
“t” – Text-Default value. Text mode
“b” – Binary- Binary Mode (e.g. images)

WORKING WITH TEXT FILES:
Basic operations with files:
a. Read the data from a file
b. Write the data to a file
c. Append the data to a file
d. Delete a file

a. Read the data from a file:
There are 3 types of functions to read data from a file.

• read( ) : reads n bytes. if no n is specified, reads the entire file.
• readline( ) : Reads a line. if n is specified, reads n bytes.
• readlines( ): Reads all lines and returns a list.

Steps to read data from a file:
• Create and Open a file using open( ) function
• use the read( ), readline( ) or readlines( ) function
• print/access the data
• Close the file.

Let a text file “Book.txt” has the following text:
“Python is interactive language. It is case sensitive language.
It makes the difference between uppercase and lowercase letters. It is official language of google.”

Example-1: Program using read( ) function:

fin=open(“D:\python programs\Book.txt”,’r’) str=fin.read( ) print(str) fin.close( )	fin=open(“D:\python programs\Book.txt”,’r’) str=fin.read(10) print(str) fin.close( )
OUTPUT: Python is interactive language. It is case sensitive language. It makes the difference between uppercase and lowercase letters. It is official language of google.	OUTPUT: Python is

Example-2: using readline( ) function:
fin=open(“D:\\python programs\\Book.txt”,’r’)
str=fin.readline( )
print(str)
fin.close( )
OUTPUT:
Python is interactive language. It is case sensitive language.
Example-3: using readlines( ) function:
fin=open(“D:\\python programs\\Book.txt”,’r’)
str=fin.readlines( )
print(str)
fin.close( )
OUTPUT:
[‘Python is interactive language. It is case sensitive language.\n’, ‘It makes the difference between uppercase and lowercase letters.\n’, ‘It is official language of google.’]

Some important programs related to read data from text files:

Program-a: Count the number of characters from a file. (Don’t count white spaces)

fin=open(“Book.txt”,’r’)
str=fin.read()
L=str.split()
count_char=0
for i in L:
count_char=count_char+len(i)
print(count_char)
fin.close( )

Program-b: Count the number of words in a file.

fin=open(“Book.txt”,’r’)
str=fin.read()
L=str.split()
count_words=0
for i in L:
count_words=count_words+1
print(count_words)
fin.close( )

Program-c: Count number of lines in a text file.

fin=open(“Book.txt”,’r’)
str=fin.readlines()
count_line=0
for i in str:
count_line=count_line+1
print(count_line)
fin.close( )

Program-d: Count number of vowels in a text file.

fin=open(“D:\\python programs\\Book.txt”,’r’)
str=fin.read()
count=0
for i in str:
if i==’a’ or i==’e’ or i==’i’ or i==’o’ or i==’u’:
count=count+1
print(count)
fin.close( )

Program-e : Count the number of ‘is’ word in a text file.

fin=open(“D:\\python programs\\Book.txt”,’r’)
str=fin.read()
L=str.split()
count=0
for i in L:
if i==’is’:
count=count+1
print(count)
fin.close( )

b. Write data to a file:

There are 2 types of functions to write the data to a file.
• write( ):Write the data to a file.
Syntax:write(string) (for text files) write(byte_string) (for binary files)
• writelines( ): Write all strings in a list L as lines to file.
To write the data to an existing file, you have to use the following mode:
“w” – Write – will overwrite any existing content

Example: Open the file “Book.txt” and append content to the file:

fout= open(“Book.txt”, “a”)
fout.write(“Welcome to the world of Programmers”)

Example: Open the file “Book.txt” and overwrite the content:

fout = open(“Book.txt”, “w”)
fout.write(“It is creative and innovative”)

Program: Write a program to take the details of book from the user and write the record in text file.

fout=open(“D:\\python programs\\Book.txt”,’w’)
n=int(input(“How many records you want to write in a file ? :”))
for i in range(n):
print(“Enter details of record :”, i+1)
title=input(“Enter the title of book : “)
price=float(input(“Enter price of the book: “))
record=title+” , “+str(price)+’\n’
fout.write(record)
fout.close( )

OUTPUT:

How many records you want to write in a file ? :3

Enter details of record : 1
Enter the title of book : java
Enter price of the book: 250
Enter details of record : 2
Enter the title of book : c++
Enter price of the book: 300
Enter details of record : 3
Enter the title of book : python
Enter price of the book: 450 img

c. Append the data to a file:

This operation is used to add the data in the end of the file. It doesn’t overwrite the existing data in a file. To write the data in the end of the file, you have to use the following mode:
“a” – Append – will append to the end of the file.

Program: Write a program to take the details of book from the user and write the record in the end of the text file.

fout=open(“D:\\python programs\\Book.txt”,’a’)
n=int(input(“How many records you want to write in a file ? :”))
for i in range(n):
print(“Enter details of record :”, i+1)
title=input(“Enter the title of book : “)
price=float(input(“Enter price of the book: “))
record=title+” , “+str(price)+’\n’
fout.write(record)

OUTPUT:

How many records you want to write in a file ? :2

Enter details of record : 1
Enter the title of book : DBMS
Enter price of the book: 350
Enter details of record : 2
Enter the title of book : Computer Networking
Enter price of the book: 360

WORKING WITH BINARY FILES:

Binary files are used to store binary data such as images,video files, audio files etc. They store data in the binary format (0’s and 1’s) .In Binary files there is no delimiter for a line. To open files in binary mode, when specifying a mode, add ‘b’ to it. Pickle module can be imported to write or read data in a binary file.

(a) Write data to a Binary File:

Example:
import pickle
e={‘Namita’:25000,’Manya’:30000,’Tanu’:20000}
f1=open(’emp.dat’,’wb’)
pickle.dump(e,f1)
f1.close()
Output:
A file named emp.dat will be created in current working directory.
(b) Read the data from Binary File:
Example:
import pickle
f1=open(’emp.dat’,’rb’)
e=pickle.load(f1)
for x in e:
print(x)
f1.close()
Output:
Namita
Manya
Tanu
Example :
import pickle
f1=open(’emp.dat’,’rb’)
e=pickle.load(f1)
for x in e:
if(e[x]>=25000 and e[x]<=30000):
print(x)
f1.close()
Output: img

tell( ) and seek( ) methods:
tell( ): It returns the current position of cursor in file.
Example:
fout=open(“story.txt”,”w”)
fout.write(“Welcome Python”)
print(fout.tell( ))
fout.close( )
Output:
14
seek(offset) : Change the cursor position by bytes as specified by the offset.
Example:
fout=open(“story.txt”,”w”)
fout.write(“Welcome Python”)
fout.seek(5)
print(fout.tell( ))
fout.close( )

Output:
5
File I/O Attributes

Attribute	Description
name	Returns the name of the file (Including path)
mode	Returns mode of the file. (r or w etc.)
encoding	Returns the encoding format of the file
closed	Returns True if the file closed else returns False

Example:
f = open(“D:\\story.txt”, “r”)
print(“Name of the File: “, f.name)
print(“File-Mode : “, f.mode)
print(“File encoding format : “, f.encoding)
print(“Is File closed? “, f.closed)
f.close()
print(“Is File closed? “, f.closed)
OUTPUT:
Name of the File: D:\story.txt File-Mode : r
File encoding format : cp1252
Is File closed? False
Is File closed? True

Relative and Absolute Paths :

• We all know that the files are kept in directory which are also known as folders.
• Every running program has a current directory. Which is generally a default directory and python always see the default directory first.
• The absolute paths are from the topmost level of the directory structure. The relative paths are relative to the current working directory denoted as a dot(.) while its parent directory is denoted with two dots(..).
• OS module provides many such functions which can be used to work with files and directories. OS means Operating System.
• getcwd( ) is a very function which can be used to identify the current working directory
>>> import os
>>> cwd=os.getcwd()
>>> print(cwd)
C:\Users\kv2kkdSrSec\AppData\Local\Programs\Python\Python36-32

STANDARD FILE STREAMS :

• We use standard I/O Streams to get better performance from different I/O devices.
• Some Standard Streams in python are as follows –
– Standard input Stream sys.stdin
– Standard output Stream sys.stdout
– Standard error Stream sys.stderr
import sys
f=open(r”hello.txt”)
line1=f.readline()
line2=f.readline()
line3=f.readline()
sys.stdout.write(line1)
sys.stdout.write(line2)
sys.stdout.write(line3)
sys.stderr.write(“\nNo errors occured\n”)
f.close()
OUTPUT:
Comp Science
Informatics Practices
Kendriya Vidyalaya AFS Salua
No errors occured