Multiple Exceptions in Python

Learn how to handle multiple types of exceptions in Python using multiple except blocks.

What are Multiple Exceptions?

A Python program can generate different types of exceptions during execution.

For example, converting invalid text into a number can cause a ValueError, while dividing a number by zero can cause a ZeroDivisionError.

Multiple exceptions allow us to handle different exceptions separately.

Multiple Exception Flow

Basic Syntax

try:

    # code that may cause an exception

except ValueError:

    # handle ValueError

except ZeroDivisionError:

    # handle ZeroDivisionError

Python checks the except blocks and executes the one that matches the exception.

Simple Example

try:

    number = int(input("Enter a number: "))

    result = 100 / number

    print(result)

except ValueError:

    print("Please enter a valid number")

except ZeroDivisionError:

    print("Cannot divide by zero")

Example Output:

Enter a number: abc
Please enter a valid number

Enter a number: 0
Cannot divide by zero

The program handles both exceptions separately.

Handling ValueError

A ValueError occurs when a value is not valid for the requested operation.

try:

    number = int("abc")

    print(number)

except ValueError:

    print("Invalid number")

Output:

Invalid number

Handling ZeroDivisionError

A ZeroDivisionError occurs when a number is divided by zero.

try:

    result = 10 / 0

    print(result)

except ZeroDivisionError:

    print("Cannot divide by zero")

Output:

Cannot divide by zero

Handling TypeError

A TypeError can occur when an operation is performed between incompatible data types.

try:

    result = "10" + 5

    print(result)

except TypeError:

    print("Invalid data types")

Output:

Invalid data types

Handling IndexError

An IndexError occurs when we try to access a list position that does not exist.

numbers = [10, 20, 30]

try:

    print(numbers[5])

except IndexError:

    print("Invalid index")

Output:

Invalid index

Handling KeyError

A KeyError occurs when a dictionary key does not exist.

student = {
    "name": "Rahul",
    "course": "Python"
}

try:

    print(student["fees"])

except KeyError:

    print("Key not found")

Output:

Key not found

Multiple Exceptions with User Input

User input can produce different exceptions, so we can handle each one separately.

try:

    first = int(
        input("Enter first number: ")
    )

    second = int(
        input("Enter second number: ")
    )

    result = first / second

    print("Result:", result)

except ValueError:

    print("Please enter numbers only")

except ZeroDivisionError:

    print("Second number cannot be zero")

This example handles both invalid input and division by zero.

Multiple Exceptions with Same Handling

If different exceptions require the same response, we can handle them inside one except block.

try:

    number = int(input("Enter a number: "))

    result = 100 / number

    print(result)

except (ValueError, ZeroDivisionError):

    print("Invalid input or division by zero")

Output:

Invalid input or division by zero

Parentheses are used to specify multiple exception types.

Using as with Multiple Exceptions

We can store the exception object in a variable using the as keyword.

try:

    number = int("abc")

except ValueError as error:

    print("Error:", error)

Output:

Error: invalid literal for int() with base 10: 'abc'

The variable error contains information about the exception.

Order of except Blocks

Python checks the except blocks from top to bottom.

Specific exception handlers should be written before a general Exception handler.

try:

    number = int("abc")

except ValueError:

    print("Invalid number")

except Exception:

    print("Some other error occurred")

Python first checks ValueError. If the exception matches, that block is executed.

Using the General Exception Class

We can use Exception to catch many standard exceptions.

try:

    result = 10 / 0

except Exception as error:

    print("Error:", error)

Use specific exception types whenever practical so that the actual problem is clear.

Example: Student Marks 👀🌍

try:

    marks = int(
        input("Enter student marks: ")
    )

    if marks < 0 or marks > 100:

        print("Marks must be between 0 and 100")

    else:

        print("Valid marks:", marks)

except ValueError:

    print("Please enter a valid number")

This example handles invalid user input using ValueError.

Best Practices

Common Mistakes

• Using the wrong exception type.
• Using a completely generic except without understanding the error.
• Putting too much code inside the try block.
• Not providing a useful error message.
• Placing a general exception handler before a specific exception handler.

Practice Programs

1. Handle ValueError and ZeroDivisionError separately.
2. Create a calculator using multiple except blocks.
3. Handle an invalid list index using IndexError.
4. Handle a missing dictionary key using KeyError.
5. Handle two exception types using one except block.
6. Print the exception message using as error.