2.1 Introduction to Files

Why Do We Need Files?

Till now, programs:

• Take input from keyboard
• Show output on screen
• Lose data once program ends

👉 Files are needed to store data permanently on secondary storage (HDD, SSD, pen drive).

Definition of File

A file is a named location on secondary storage used to store data permanently.

📌 Python programs themselves are stored as files with .py extension.

Real-Life Examples

• Employee records
• Student databases
• Inventory systems
• Log files

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2.2 Types of Files

Python mainly deals with two types of files:

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🔸 2.2.1 Text Files

Text files contain human-readable characters.

📌 Examples:

• .txt
• .py
• .csv

Characteristics

• Stored as ASCII / Unicode characters
• Can be opened in Notepad, VS Code
• Each line ends with newline character \n

Example

Hello Python
Welcome to File Handling

📌 Internally stored as binary (0s and 1s) but displayed as readable text.

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🔸 2.2.2 Binary Files

Binary files contain non-human-readable data.

📌 Examples:

• .jpg
• .mp3
• .mp4
• .exe
• .dat

Characteristics

• Opened using specific programs
• Even a single-bit change can corrupt the file
• Used for images, videos, objects

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2.3 Opening and Closing a Text File

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🔸 Opening a File

Python uses the open() function.

Syntax

file_object = open(file_name, mode)

📌 file_object → file handle 📌 mode → how the file is accessed

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🔸 File Opening Modes (Very Important)

Mode	Meaning
r	Read (default)
w	Write (overwrites file)
a	Append
r+	Read + Write
a+	Append + Read
b	Binary mode

Example

f = open("data.txt", "r")

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🔸 Closing a File

Always close a file to:

• Save data
• Free memory

Syntax

f.close()

📌 Python flushes buffered data before closing.

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🔸 Using with Statement (BEST PRACTICE)

Automatically closes the file.

with open("data.txt", "r") as f:
    content = f.read()

✔ No need for close() ✔ Safe even if exception occurs

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2.4 Writing to a Text File

To write data, file must be opened in:

• w (write)
• a (append)

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🔸 write() Method

Writes a single string.

f = open("sample.txt", "w")
f.write("Welcome to Python\n")
f.write("File Handling Chapter")
f.close()

📌 Returns number of characters written.

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🔸 writelines() Method

Writes multiple strings.

lines = ["Apple\n", "Banana\n", "Mango\n"]
f = open("fruits.txt", "w")
f.writelines(lines)
f.close()

📌 No automatic newline → must add \n

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2.5 Reading from a Text File

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🔸 read() Method

Reads entire file.

f = open("sample.txt", "r")
data = f.read()
print(data)
f.close()

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🔸 read(n) Method

Reads n characters.

print(f.read(10))

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🔸 readline() Method

Reads one line at a time.

f = open("sample.txt")
print(f.readline())
print(f.readline())
f.close()

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🔸 readlines() Method

Reads all lines as a list.

f = open("sample.txt")
lines = f.readlines()
print(lines)
f.close()

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2.6 Setting Offsets in a File

File pointer determines current position.

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🔸 tell() Method

Returns current position.

f = open("sample.txt")
print(f.tell())

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🔸 seek() Method

Moves file pointer.

f.seek(0)     # Beginning
f.seek(5)     # Move to 5th byte

📌 Syntax:

f.seek(offset, reference)

Reference	Meaning
0	Beginning
1	Current position
2	End of file

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2.7 Creating and Traversing a Text File

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🔸 Creating a File

Opening in w or a creates file automatically.

f = open("newfile.txt", "w")
f.write("File created successfully")
f.close()

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🔸 Traversing a File (Line by Line)

f = open("sample.txt", "r")
for line in f:
    print(line, end="")
f.close()

✔ Most efficient method ✔ Exam-favourite program

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2.8 The Pickle Module

Used for binary file handling.

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🔸 Why Pickle?

• Stores Python objects directly
• Faster than text files
• Used for lists, dictionaries, custom objects

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🔸 Writing Data using Pickle

import pickle

data = ["Python", "Java", "C++"]

f = open("lang.dat", "wb")
pickle.dump(data, f)
f.close()

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🔸 Reading Data using Pickle

import pickle

f = open("lang.dat", "rb")
data = pickle.load(f)
print(data)
f.close()

📌 File must be opened in binary mode (wb, rb)

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📝 NCERT EXAM SUMMARY (Must Remember)

• Files provide permanent storage
• Text files → human readable
• Binary files → machine readable
• with statement → safest way
• write() ≠ writelines()
• seek() controls pointer
• pickle → object serialization

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Board-Level Solved Programs (Chapter 2)

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Program 1: Create and Write to a Text File

f = open("data.txt", "w")
f.write("Welcome to File Handling\n")
f.write("CBSE Class 12 Computer Science")
f.close()

📌 Concept: File creation, write()

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Program 2: Read Entire File Using read()

f = open("data.txt", "r")
content = f.read()
print(content)
f.close()

📌 Concept: read()

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Program 3: Read File Line by Line (readline())

f = open("data.txt", "r")
print(f.readline())
print(f.readline())
f.close()

📌 Concept: readline()

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Program 4: Read All Lines Using readlines()

f = open("data.txt", "r")
lines = f.readlines()
print(lines)
f.close()

📌 Concept: List of lines

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Program 5: Append Data to an Existing File

f = open("data.txt", "a")
f.write("\nThis line is appended")
f.close()

📌 Concept: Append mode (a)

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Program 6: Write Multiple Lines Using writelines()

lines = ["Python\n", "Java\n", "C++\n"]
f = open("languages.txt", "w")
f.writelines(lines)
f.close()

📌 Note: No automatic newline

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Program 7: Count Number of Lines in a File

f = open("data.txt", "r")
count = 0
for line in f:
    count += 1
f.close()
print("Number of lines:", count)

📌 Very common exam program

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Program 8: Count Words in a File

f = open("data.txt", "r")
words = 0
for line in f:
    words += len(line.split())
f.close()
print("Number of words:", words)

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Program 9: Count Characters in a File

f = open("data.txt", "r")
text = f.read()
f.close()
print("Characters:", len(text))

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Program 10: Search a Word in a File

f = open("data.txt", "r")
word = "Python"
found = False

for line in f:
    if word in line:
        found = True
        break

f.close()

if found:
    print("Word found")
else:
    print("Word not found")

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Program 11: Copy Contents from One File to Another

f1 = open("data.txt", "r")
f2 = open("copy.txt", "w")

f2.write(f1.read())

f1.close()
f2.close()

📌 Classic CBSE program

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Program 12: Read File Using with Statement

with open("data.txt", "r") as f:
    print(f.read())

📌 Best practice

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Program 13: Display Lines Starting with a Vowel

f = open("data.txt", "r")
for line in f:
    if line[0].lower() in "aeiou":
        print(line, end="")
f.close()

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Program 14: Use of tell()

f = open("data.txt", "r")
print(f.tell())
f.read(10)
print(f.tell())
f.close()

📌 Concept: File pointer position

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Program 15: Use of seek()

f = open("data.txt", "r")
f.seek(5)
print(f.read())
f.close()

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Program 16: Handle File Not Found Exception

try:
    f = open("abc.txt", "r")
    print(f.read())
except FileNotFoundError:
    print("File does not exist")

📌 Links Chapter 1 + 2

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Program 17: Store List Using Pickle

import pickle

data = [10, 20, 30, 40]
f = open("numbers.dat", "wb")
pickle.dump(data, f)
f.close()

📌 Binary file

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Program 18: Read List from Pickle File

import pickle

f = open("numbers.dat", "rb")
data = pickle.load(f)
f.close()
print(data)

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Program 19: Store Dictionary Using Pickle

import pickle

student = {"Roll": 1, "Name": "Amit", "Marks": 92}
f = open("student.dat", "wb")
pickle.dump(student, f)
f.close()

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Program 20: Read Dictionary from Pickle File

import pickle

f = open("student.dat", "rb")
student = pickle.load(f)
f.close()
print(student)

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CBSE 2025 CASE-STUDY QUESTIONS (Chapter 2)

Case Study 1: School Record System

A school stores student records in a text file.

Questions:

1. Which file mode is used to add new records without deleting old data? ✔ a

2. Write a program to count total students stored in the file.

   f = open("students.txt", "r")
   count = 0
   for line in f:
   count += 1
   f.close()
   print("Total students:", count)
   

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Case Study 2: Library Management System

Library books are stored in a file books.txt.

1. How will you check if a book exists?

   f = open("books.txt", "r")
   book = input("Enter book name: ")
   found = False
   
   for line in f:
   if book in line:
       found = True
       break
   
   f.close()
   
   if found:
   print("Book available")
   else:
   print("Book not available")
   

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Case Study 3: Log File Analysis

A log file records user activities.

1. Which method reads the file line by line efficiently? ✔ for line in file

2. Why is with preferred?

✔ Automatically closes file, prevents data loss.

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Case Study 4: Student Result Processing

Student marks are stored using pickle.

1. Why use pickle instead of text file?

✔ Stores Python objects directly ✔ Faster and safer

1. Write code to read the stored object.

   import pickle
   f = open("result.dat", "rb")
   data = pickle.load(f)
   f.close()
   print(data)
   

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Case Study 5: Data Security Scenario

Old hard disks are discarded without deleting files properly.

1. What is the risk? ✔ Data recovery by unauthorized users

2. How can this be prevented? ✔ Proper data deletion / shredding tools

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