Sometimes, programs run into errors (called exceptions) that stop them from working. Instead of letting the program crash, we can use try-except to catch these errors and handle them properly.

For example, dividing a number by zero will cause an error:

print(10 / 0)  # This will crash with a "ZeroDivisionError"

With try-except, we can prevent the crash and show a helpful message instead.

Basic `try-except` syntax

A try-except block has two parts:

try: The code that might cause an error.
except: What to do if an error happens.

Example:

try:
    print(10 / 0)  # This might cause an error
except:
    print("Oops! Something went wrong.")  # This runs if an error happens

Output:

Oops! Something went wrong.

Even though there’s an error, the program does not crash because except handles it.

Handling multiple Exceptions

Different errors need different solutions. We can catch specific errors using multiple except blocks.

Example:

try:
    num = int(input("Enter a number: "))  # Might cause a ValueError
    result = 10 / num  # Might cause a ZeroDivisionError
    print("Result:", result)
except ValueError:
    print("Please enter a valid number!")  
except ZeroDivisionError:
    print("You can't divide by zero!")

Example outputs:

Enter a number: abc  
Please enter a valid number!

Enter a number: 0  
You can't divide by zero!

Each except block handles a different type of error.

Using `except Exception as e` for debugging

Sometimes, we don’t know what error might happen. We can use except Exception as e to catch any error and see its message.

Example:

try:
    print(10 / 0)
except Exception as e:
    print("Error:", e)  # Shows the actual error message

Output:

Error: division by zero

This is useful for debugging because it tells us exactly what went wrong.

Summary:

try-except helps prevent crashes by handling errors.
We can catch specific errors using multiple except blocks.
except Exception as e helps with debugging.

Hands-On Practise

Exercise: Handling Exceptions in a Function

Write a function called safe_divide(a, b) that:

Tries to divide a by b.
Catches ZeroDivisionError if b is zero and prints "You can't divide by zero!".
Catches TypeError if a or b is not a number and prints "Please provide numbers only!".
Catches any other error using except Exception as e and prints the actual error message.

Expected Output Examples

Valid division:

safe_divide(10, 2)

Result: 5.0

Division by zero:

safe_divide(10, 0)

You can't divide by zero!

Wrong data type:

safe_divide(10, "abc")

Please provide numbers only!

Unexpected error (e.g., passing a list):

safe_divide([10], 2)

An unexpected error occurred: unsupported operand type(s) for /: 'list' and 'int'

Your Task:

Complete the function by filling in the missing parts (????).

def safe_divide(a, b):
    try:
        result = ????  # Perform division
        print("Result:", result)
    except ????:
        print("You can't divide by zero!")
    except ????:
        print("Please provide numbers only!")
    except ???? as e:
        print("An unexpected error occurred:", e)

# Test cases
safe_divide(10, 2)
safe_divide(10, 0)
safe_divide(10, "abc")
safe_divide([10], 2)

Bonus Challenge: Add a finally: block that prints "Operation complete." every time the function runs.

Output:

Quizzes: 0/5

Question 1:

What does a try-except block do in Python?

It handles errors without stopping the program.
It is used to define variables.
It performs mathematical operations.
It creates a new function in Python.

Question 2:

What will happen if you try to divide a number by zero in a try block?

The program will crash.
A `ZeroDivisionError` will be raised, and the `except` block will handle it.
Python will ignore the error and continue.
A `TypeError` will be raised.

Question 3:

Which exception is best for handling input errors when the user enters a non-numeric value?

ValueError
IndexError
TypeError
FileNotFoundError

Question 4:

What is the purpose of the except Exception as e block?

It catches any error and stores the error message in `e`.
It is used to print the error message only.
It helps to perform mathematical operations.
It stops the program completely.

Question 5:

What is the output if you run the following code? try: print(10 / 0) except ZeroDivisionError: print('Cannot divide by zero')

Cannot divide by zero
ZeroDivisionError
None
An unexpected error occurred

2. Handling Exceptions with try-except
Quiz: 0/5

Basic `try-except` syntax

Handling multiple Exceptions

Example:

Using `except Exception as e` for debugging

Example:

Summary:

Hands-On Practise

Exercise: Handling Exceptions in a Function

Expected Output Examples

Your Task:

Quizzes: 0/5

What does a try-except block do in Python?

What will happen if you try to divide a number by zero in a try block?

Which exception is best for handling input errors when the user enters a non-numeric value?

What is the purpose of the except Exception as e block?

What is the output if you run the following code? try: print(10 / 0) except ZeroDivisionError: print('Cannot divide by zero')

Feedback

Discussion

2. Handling Exceptions with try-exceptQuiz: 0/5

Basic try-except syntax

Handling multiple Exceptions

Example:

Using except Exception as e for debugging

Example:

Summary:

Hands-On Practise

Exercise: Handling Exceptions in a Function

Expected Output Examples

Your Task:

Quizzes: 0/5

What does a try-except block do in Python?

What will happen if you try to divide a number by zero in a try block?

Which exception is best for handling input errors when the user enters a non-numeric value?

What is the purpose of the except Exception as e block?

What is the output if you run the following code? try: print(10 / 0) except ZeroDivisionError: print('Cannot divide by zero')

Feedback

Discussion

2. Handling Exceptions with try-except
Quiz: 0/5

Basic `try-except` syntax

Using `except Exception as e` for debugging