NCERT Class 12 Computer Science Chapter 1 Book PDF Download

The NCERT Class 12 Computer Science Book PDF Chapter 1 Exception Handling in Python opens the Class 12 course and runs to about 18 pages in the 2026-27 reprint. The chapter explains how Python deals with errors at runtime, building from syntax errors to built-in exceptions, the raise and assert statements, and the full try / except / else / finally block.

• Seven numbered sections (1.1 to 1.7) with screenshots from the Python shell, Table 1.1 of built-in exceptions, and Program 1-1 on the assert statement.
• Free, unmodified official NCERT textbook PDF for offline reading, mapped to the 2026-27 CBSE Class 12 Computer Science syllabus.

This page hosts the official NCERT Class 12 Computer Science Chapter 1 textbook PDF as released by NCERT, with no edits, no watermark, and no advertising on the pages, curated by Collegedunia subject experts for the 2026-27 CBSE syllabus.

What the NCERT Class 12 Computer Science Book PDF Chapter 1 Exception Handling in Python Covers

The downloadable file above is the original Chapter 1 from the NCERT Class 12 Computer Science textbook, published by the National Council of Educational Research and Training. It is the same printed text used by CBSE-affiliated schools across India and the source for every internal and board question on exception handling. The chapter answers one core question: what does Python do when a program hits an error, and how can a programmer take control of that error instead of letting the program crash.

• Errors at three stages: syntax errors caught before the program runs, and runtime and logical errors that surface during execution.
• Exceptions as objects: an exception is a Python object that represents an error, and it can be raised automatically or forced by the programmer.
• Built-in exceptions: Table 1.1 lists 12 common ones such as ValueError, ZeroDivisionError, NameError, and IOError.
• Forcing and handling: the raise and assert statements throw exceptions, while the try block with except, else, and finally catches and handles them.

Because this chapter sets up the error-handling vocabulary used in File Handling, database work, and every later program, a clean first read here saves time across the whole course.

Chapter 1 Exception Handling Section Sequence (1.1 to 1.7)

The chapter is organised into seven numbered sections that the textbook builds in a deliberate teaching order: first what an error is, then how Python reports it, and finally how the programmer takes control. The table below maps each section to its content and the answer style CBSE rewards.

Sections 1.4, 1.6, and 1.7 carry the heaviest exam load. Most board questions ask you to name the right built-in exception or to complete a try / except / finally block.

Syntax Errors vs Exceptions in Python

The chapter opens by drawing a clean line between the two kinds of problems. A syntax error is broken grammar: you forgot a colon, a bracket, or a quote, so Python cannot even read the program. It is caught before any line runs. An exception is a problem that appears while a syntactically correct program is running, such as dividing by zero or opening a file that does not exist.

• Syntax error: detected at parse time, the program does not execute at all until you fix it.
• Exception: detected at runtime in a valid program, and it can be caught and handled in code.
• The textbook notes that SyntaxError is itself a kind of exception, which is why every syntax error is an exception, but not every exception is a syntax error.

>>> if marks > 20          # missing colon
SyntaxError: invalid syntax     # caught before the program runs

>>> print(50 / 0)          # valid grammar, fails while running
ZeroDivisionError: division by zero   # an exception at runtime

Built-in Exceptions in Python: Table 1.1 Explained

Section 1.4 gives Table 1.1, the single most quoted table in the chapter. These are exceptions that Python already defines, so you do not have to create them. Learning the common ones by name turns several 1-mark and 2-mark questions into easy marks, because the exam often shows a short program and asks which exception it raises.

The chapter also lists KeyboardInterrupt, EOFError, IndentationError, and OverFlowError in the full Table 1.1. A programmer can also build user-defined exceptions for their own needs.

Raising Exceptions in Python: the raise and assert Statements

Section 1.5 shows how a programmer can force an exception instead of waiting for Python to find one. This is called throwing an exception, and the chapter gives two ways to do it. Once an exception is raised, no further statement in that block runs, so control jumps to the handler.

The raise statement

The raise statement throws an exception on demand. Its syntax is raise exception-name[(optional argument)], where the argument is the message shown when the exception is raised. It is useful when your own logic decides a value is invalid, such as a denominator of zero.

num1 = int(input("Enter the numerator: "))
num2 = int(input("Enter the denominator: "))
if num2 == 0:
    raise ZeroDivisionError("Denominator cannot be zero")
print("Quotient =", num1 / num2)

The assert statement

The assert statement tests an expression. If the expression is false, Python raises an AssertionError, which you can handle like any other exception. Its syntax is assert Expression[, arguments]. The chapter uses it in Program 1-1 to check for a non-negative number.

def negativecheck(number):
    assert (number >= 0), "OOPS... Negative Number"
    print(number * number)

print(negativecheck(100))      # prints 10000
print(negativecheck(-350))     # raises AssertionError: OOPS... Negative Number

Tip: Use raise when you want to throw a specific named exception, and assert when you want a quick sanity check on a value at the start of a function.

Handling Exceptions in Python: try, except, else and finally

Section 1.6 and Section 1.7 cover the part the exam tests most: catching an exception so the program keeps running. The risky code goes inside a try block, and the recovery code goes inside one or more except blocks. The optional else runs only if no exception was raised, and the finally block runs no matter what.

• try: holds the statements that might raise an exception.
• except: catches a named exception and runs the handler code.
• else: runs only when the try block finished with no exception.
• finally: always runs at the end, used to release resources such as closing a file.

print("Learning Exceptions...")
try:
    num1 = int(input("Enter the first number: "))
    num2 = int(input("Enter the second number: "))
    quotient = num1 / num2
    print("Both the numbers entered were correct")
except ValueError:                 # entered something that is not an integer
    print("Please enter only numbers")
except ZeroDivisionError:          # denominator was zero
    print("Number 2 should not be zero")
else:
    print("Great.. you are a good programmer")
finally:                           # runs at the end no matter what
    print("JOB OVER... GO GET SOME REST")

If the user types a letter, ValueError fires; if the second number is zero, ZeroDivisionError fires; if both inputs are valid, the else branch runs. In every case the finally line prints, which is the behaviour board questions like to test.

Class 12 Computer Science Chapter 1 Exam Weightage and Question Trends

Exception Handling is a high-yield chapter for short answers. In the CBSE Class 12 Computer Science board paper it usually shows up as a fill-in-the-blank try block, a name the exception question, or a short program using raise or finally. The table below maps the asked question types across recent board cycles.

Across the last five board cycles, a try / except question has appeared in four out of five papers. Treat the full block, including else and finally, as compulsory revision before the exam.

How to Use the NCERT Book PDF Chapter 1 for Board Prep

This PDF is your primary reading text. The chapter is short, so the best plan is two passes: one to learn the vocabulary, one to practise the blocks by hand. The supporting Collegedunia resources fit around these two passes.

First pass: learn the words (45 minutes)

Read sections 1.1 to 1.4 and note the difference between an error and an exception, then learn Table 1.1 by name. Write one line of meaning next to each built-in exception so the names stick before you try to use them.

Second pass: write the blocks (1 to 1.5 hours)

Work through sections 1.5 to 1.7 by typing the raise, assert, and full try / except / else / finally examples yourself. Then attempt the nine end-of-chapter exercise questions and verify each answer against the Class 12 Computer Science Chapter 1 NCERT Solutions linked below.

JEE and CUET angle

For students sitting competitive exams, error handling appears in programming sections of JEE-level coding rounds and in CUET Computer Science. The try / except pattern and the named built-in exceptions here carry over directly, so this chapter doubles as competitive prep.

NCERT Class 12 Computer Science Book PDF Chapter 1: Key Features of the Official Print

• Reprint Edition: 2026-27, aligned to the current CBSE syllabus with no chapter content trimmed.
• Publisher: National Council of Educational Research and Training, New Delhi.
• Pages: About 18 pages, covering sections 1.1 to 1.7 plus nine end-of-chapter exercise questions.
• Licence: Open educational resource, free for student download and classroom use.
• File Type: Searchable text PDF, mobile-readable, print-ready at A4 size.

Other Resources for Class 12 Computer Science Chapter 1 Exception Handling in Python

Pair this NCERT Book PDF with the matching revision notes, handwritten notes, and the step-by-step NCERT Solutions. All resources for Class 12 Computer Science Chapter 1 Exception Handling in Python are linked below.

NCERT Book PDF for Class 12 Computer Science: All Chapters

Related Links: Use the table below to download the official NCERT Book PDF for the other chapters of Class 12 Computer Science. Every chapter ships as the unmodified NCERT print for the 2026-27 syllabus.