Handling specific exceptions in Python - Mini Project: Build & Apply

Handling specific exceptions

📖 Scenario: Imagine you are writing a small program that asks a user to enter two numbers and divides the first number by the second. Sometimes users might enter wrong data or try to divide by zero, which causes errors. We want to handle these errors carefully so the program does not crash and gives friendly messages.

🎯 Goal: You will build a program that safely divides two numbers by handling specific errors: ValueError when the input is not a number, and ZeroDivisionError when dividing by zero.

📋 What You'll Learn

Create two variables to store user input as numbers

Add a try-except block to catch ValueError and ZeroDivisionError

Print a friendly message for each specific error

Print the division result if no error occurs

💡 Why This Matters

🌍 Real World

Handling specific exceptions helps programs run smoothly even when users make mistakes, like entering wrong data or dividing by zero.

💼 Career

Knowing how to catch and handle errors is essential for writing reliable software that does not crash unexpectedly.

1

DATA SETUP: Create variables for user input

Create two variables called num1 and num2 by converting the strings '10' and '0' to integers using int().

Python

# Create variables num1 and num2 from strings '10' and '0'
# Your code here

Hint

Use int('10') to convert the string '10' to the number 10.

2

CONFIGURATION: Prepare for error handling

Create a variable called result and set it to None. This will hold the division result later.

Python

num1 = int('10')
num2 = int('0')
# Create a variable result and set it to None
# Your code here

Hint

Set result = None before trying the division.

3

CORE LOGIC: Use try-except to handle specific exceptions

Write a try block where you divide num1 by num2 and assign it to result. Add two except blocks: one for ZeroDivisionError that prints 'Cannot divide by zero.' and one for ValueError that prints 'Invalid number input.'.

Python

num1 = int('10')
num2 = int('0')
result = None
# Use try-except to divide num1 by num2
# Your code here

Hint

Put the division inside try: and catch errors with except ZeroDivisionError: and except ValueError:.

4

OUTPUT: Print the division result if no error

After the try-except blocks, write an if statement that checks if result is not None. If so, print f'Result: {result}' to show the division result.

Python

num1 = int('10')
num2 = int('0')
result = None
try:
    result = num1 / num2
except ZeroDivisionError:
    print('Cannot divide by zero.')
except ValueError:
    print('Invalid number input.')
# Print the result if it is not None
# Your code here

Hint

Use if result is not None: to check before printing.

Practice

1. What is the main purpose of using try-except blocks in Python?

easy

A. To catch and handle specific errors so the program doesn't crash

B. To speed up the program execution

C. To write comments inside the code

D. To create new functions automatically

Solution

1. Step 1: Understand the role of try-except

   The try-except block is used to catch errors that happen during program execution.

2. Step 2: Identify the benefit of catching errors

   By catching errors, the program can handle them gracefully and continue running instead of crashing.

3. Final Answer:

   To catch and handle specific errors so the program doesn't crash -> Option A

4. Quick Check:

   try-except = catch errors [OK]

Hint: Try-except blocks catch errors to avoid crashes [OK]

Common Mistakes:

• Thinking try-except speeds up code
• Confusing try-except with comments
• Believing try-except creates functions

2. Which of the following is the correct syntax to catch a ZeroDivisionError in Python?

easy

A. try:
x = 1/0
except:
print('Error')

B. try:
x = 1/0
catch ZeroDivisionError:
print('Cannot divide by zero')

C. try:
x = 1/0
except ZeroDivisionError:
print('Cannot divide by zero')

D. try:
x = 1/0
except ZeroDivision:
print('Cannot divide by zero')

Solution

1. Step 1: Check the correct keyword for catching exceptions

   Python uses except to catch exceptions, not catch.

2. Step 2: Verify the exception name spelling

   The correct exception name is ZeroDivisionError, not ZeroDivision.

3. Final Answer:

   try: x = 1/0 except ZeroDivisionError: print('Cannot divide by zero') -> Option C

4. Quick Check:

   Use except + exact exception name [OK]

Hint: Use except with exact exception name to catch errors [OK]

Common Mistakes:

• Using 'catch' instead of 'except'
• Misspelling exception names
• Using generic except without specifying error

3. What will be the output of this code?

try:
    num = int('abc')
except ValueError:
    print('Value error caught')
except TypeError:
    print('Type error caught')

medium

A. Value error caught

B. Type error caught

C. No output

D. Program crashes with ValueError

Solution

1. Step 1: Identify the error raised by int('abc')

   Trying to convert 'abc' to int raises a ValueError.

2. Step 2: Match the error with except blocks

   The ValueError is caught by the first except block, so it prints 'Value error caught'.

3. Final Answer:

   Value error caught -> Option A

4. Quick Check:

   int('abc') = ValueError caught [OK]

Hint: Match error type to except block to find output [OK]

Common Mistakes:

• Confusing ValueError with TypeError
• Thinking program crashes without except
• Assuming no output if error caught

4. Find the error in this code and choose the correct fix:

try:
    print(10 / 0)
except ZeroDivisionError, e:
    print('Error:', e)

medium

A. Use except ZeroDivisionError(e):

B. Change except line to: except ZeroDivisionError as e:

C. Change print to print('Error') only

D. Remove the except block completely

Solution

1. Step 1: Identify the syntax error in except clause

   Python 3 requires 'as' to assign exception to a variable, not a comma.

2. Step 2: Correct the except syntax

   Replace except ZeroDivisionError, e: with except ZeroDivisionError as e:.

3. Final Answer:

   Change except line to: except ZeroDivisionError as e: -> Option B

4. Quick Check:

   Use 'as' to assign exception variable [OK]

Hint: Use 'except Exception as e:' syntax in Python 3 [OK]

Common Mistakes:

• Using comma instead of 'as' in except
• Removing except block causing crash
• Wrong parentheses in except clause

5. You want to handle both KeyError and IndexError in the same block. Which is the best way to write the except clause?

hard

A. except KeyError, IndexError:
print('Error caught')

B. except KeyError or IndexError:
print('Error caught')

C. except KeyError and IndexError:
print('Error caught')

D. except (KeyError, IndexError):
print('Error caught')

Solution

1. Step 1: Understand how to catch multiple exceptions

   Python requires a tuple of exceptions inside parentheses to catch multiple exceptions in one block.

2. Step 2: Identify correct tuple syntax

   The correct syntax is except (KeyError, IndexError): to catch both exceptions.

3. Final Answer:

   except (KeyError, IndexError): print('Error caught') -> Option D

4. Quick Check:

   Use tuple in except to catch multiple exceptions [OK]

Hint: Use except (Error1, Error2): to catch multiple exceptions [OK]

Common Mistakes:

• Using 'or' or 'and' instead of tuple
• Using comma without parentheses
• Trying to catch exceptions separately without blocks