Question 1

“Every syntax error is an exception but every exception cannot be a syntax error.” Justify the statement.

Accepted Answer

A syntax error occurs when the code violates the rules of the programming language grammar, such as missing a colon or parentheses. These errors are detected by the interpreter before the program runs and are a type of exception. However, exceptions also include runtime errors like division by zero or file not found, which are not syntax errors but logical or runtime errors. Therefore, every syntax error is an exception because it disrupts normal execution, but not every exception is a syntax error since exceptions also include runtime errors. — Syntax errors are a subset of exceptions that occur due to incorrect code structure. Exceptions include all errors that disrupt normal flow, including runtime errors. Hence, all syntax errors are exceptions, but exceptions can also be other types of errors.

Question 2

When are the following built-in exceptions raised? Give examples to support your answers.
a) ImportError
b) IOError
c) NameError
d) ZeroDivisionError

Accepted Answer

a) ImportError: Raised when an import statement fails to find the module definition or when a module cannot be loaded.
Example:
try:
    import non_existent_module
except ImportError:
    print("Module not found")

b) IOError: Raised when an input/output operation fails, such as failing to open a file.
Example:
try:
    f = open('non_existent_file.txt')
except IOError:
    print("File not found or can't be opened")

c) NameError: Raised when a local or global name is not found.
Example:
try:
    print(undefined_variable)
except NameError:
    print("Variable not defined")

d) ZeroDivisionError: Raised when division or modulo by zero takes place.
Example:
try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero") — Each exception is raised under specific conditions:
- ImportError: when import fails
- IOError: when file operations fail
- NameError: when an undefined variable is accessed
- ZeroDivisionError: when dividing by zero
Examples demonstrate typical scenarios causing these exceptions.

Question 3

What is the use of a raise statement? Write a code to accept two numbers and display the quotient. Appropriate exception should be raised if the user enters the second number (denominator) as zero (0).

Accepted Answer

The raise statement is used to explicitly throw an exception in Python. It allows the programmer to trigger an exception manually.

Example code:

try:
    num1 = float(input("Enter first number: "))
    num2 = float(input("Enter second number: "))
    if num2 == 0:
        raise ZeroDivisionError("Denominator cannot be zero")
    quotient = num1 / num2
    print("Quotient is", quotient)
except ZeroDivisionError as e:
    print("Error:", e)
except ValueError:
    print("Please enter valid numbers") — The raise statement is used to throw an exception when a specific condition occurs, such as division by zero. The code accepts two numbers, checks if the denominator is zero, raises ZeroDivisionError if so, otherwise performs division and prints the quotient.

Question 4

Use assert statement in Question No. 3 to test the division expression in the program.

Accepted Answer

The assert statement is used to test if a condition is true. If the condition is false, it raises an AssertionError.

Modified code using assert:

try:
    num1 = float(input("Enter first number: "))
    num2 = float(input("Enter second number: "))
    assert num2 != 0, "Denominator cannot be zero"
    quotient = num1 / num2
    print("Quotient is", quotient)
except AssertionError as e:
    print("Error:", e)
except ValueError:
    print("Please enter valid numbers") — The assert statement checks that the denominator is not zero before performing division. If num2 is zero, it raises an AssertionError with the message. This is an alternative to raising exceptions explicitly.

Question 5

Define the following:
a) Exception Handling
b) Throwing an exception
c) Catching an exception

Accepted Answer

a) Exception Handling: It is the process of responding to the occurrence of exceptions (errors) during the execution of a program to prevent the program from crashing.

b) Throwing an exception: It means explicitly causing an exception to occur using the raise statement.

c) Catching an exception: It means handling the exception using try and except blocks to prevent the program from terminating abruptly. — Definitions clarify the concepts:
- Exception Handling manages errors gracefully.
- Throwing an exception is generating an error intentionally.
- Catching an exception is intercepting and managing errors.

Question 6

Explain catching exceptions using try and except block.

Accepted Answer

Catching exceptions using try and except blocks involves placing the code that might raise an exception inside a try block. If an exception occurs, the control is transferred to the except block where the exception can be handled gracefully.

Example:

try:
    x = int(input("Enter a number: "))
    y = 10 / x
    print(y)
except ZeroDivisionError:
    print("Cannot divide by zero")
except ValueError:
    print("Invalid input")

This prevents the program from crashing and allows for error messages or alternative flows. — The try block contains code that may cause exceptions. The except block catches specific exceptions and handles them, ensuring the program continues or terminates gracefully.

Question 7

Consider the code given below and fill in the blanks.

```python
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 __________ : # to enter only integers
print("Please enter only numbers")
except __________ : # Denominator should not be zero
print("Number 2 should not be zero")
else:
print("Great .. you are a good programmer")
__________ : # to be executed at the end
print("JOB OVER... GO GET SOME REST")
```

Accepted Answer

The blanks should be filled as follows:

except ValueError:  # to enter only integers
except ZeroDivisionError:  # Denominator should not be zero
finally:  # to be executed at the end

Complete code:

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:
    print("Please enter only numbers")
except ZeroDivisionError:
    print("Number 2 should not be zero")
else:
    print("Great .. you are a good programmer")
finally:
    print("JOB OVER... GO GET SOME REST") — ValueError is raised when input cannot be converted to int, ZeroDivisionError when denominator is zero, and finally block executes regardless of exceptions.

Question 8

You have learnt how to use math module in Class XI. Write a code where you use the wrong number of arguments for a method (say sqrt() or pow()). Use the exception handling process to catch the ValueError exception.

Accepted Answer

Example code:

import math

try:
    # Calling sqrt() with two arguments instead of one
    result = math.sqrt(16, 4)
except TypeError as e:
    print("Error:", e)

# Alternatively, if ValueError is expected (e.g., sqrt of negative number):
try:
    result = math.sqrt(-4)
except ValueError as e:
    print("Error:", e)

Explanation:
Passing wrong number of arguments to math.sqrt() raises TypeError, which can be caught using try-except. Passing invalid values (like negative number) raises ValueError. — The math.sqrt() function expects exactly one argument. Passing two arguments raises TypeError. Passing invalid values raises ValueError. Exception handling with try-except can catch these errors and prevent program crash.

Question 9

What is the use of finally clause? Use finally clause in the problem given in Question No. 7.

Accepted Answer

The finally clause is used to specify a block of code that will be executed no matter whether an exception is raised or not. It is typically used for cleanup actions like closing files or releasing resources.

Using finally in Question 7's code:

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:
    print("Please enter only numbers")
except ZeroDivisionError:
    print("Number 2 should not be zero")
else:
    print("Great .. you are a good programmer")
finally:
    print("JOB OVER... GO GET SOME REST") — The finally block executes after try, except, and else blocks, regardless of exceptions. It ensures that certain code always runs, useful for cleanup or final messages.

Question 10

Which of the following best describes a syntax error in Python?

Accepted Answer

An error caused by violating the rules of Python syntax, preventing program execution — A syntax error occurs when the programmer does not follow the rules of the Python language, causing the interpreter to halt execution until the error is fixed. It is also called a parsing error.

Question 11

What will happen if a Python program contains a syntax error when run in script mode?

Accepted Answer

A dialog box will appear showing the error name and description, and the program will not execute — In script mode, when a syntax error is detected, Python displays a dialog box with the error name and description, and the program does not execute until the error is corrected.

Question 12

Which of the following is true about exceptions in Python?

Accepted Answer

Exceptions are errors that occur during execution despite correct syntax — Exceptions occur when a syntactically correct program encounters an error during execution, such as division by zero or file not found.

Question 13

Which built-in exception is raised when a division by zero occurs in Python?

Accepted Answer

ZeroDivisionError — ZeroDivisionError is raised when the denominator in a division operation is zero.

Question 14

What exception is raised when a Python program tries to access an index that is out of range in a list?

Accepted Answer

IndexError — IndexError is raised when the index or subscript in a sequence is out of range.

Question 15

Which built-in exception is raised when a Python program tries to open a file that does not exist?

Accepted Answer

IOError — IOError is raised when the file specified in a program statement cannot be opened.

h apter

h apter — Study Notes

1.1 INTRODUCTION

1.2 SYNTAX ERRORS

1.3 EXCEPTIONS

Practice Questions — h apter

All 13 Chapters in Computer Science