Exception Handling in Python

In Python, an exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions.

When an exception occurs, it is typically represented as an object that contains information about the error, such as its type and a message describing the error.

Python provides a robust exception handling mechanism that allows us to handle exceptions gracefully, preventing our program from crashing and providing opportunities to recover from errors.

Handling Exceptions:

We can handle exceptions using the try, except, else, and finally blocks.

Example:

try:
    # Code that may raise an exception
    result = 30 / 0

except ZeroDivisionError:
    # Handle the specific exception
    print("Error: Division by zero!")

else:
    # Executes if no exception occurred
    print("No exception occurred!")

finally:
    # Executes regardless of whether an exception occurred or not
    print("Finally block executed.")

Catch Multiple Exceptions:

We can catch multiple exceptions by providing multiple except blocks or by using a tuple of exception types:

Example:

try:
    # Code that may raise an exception
    result = int(input("Enter a number: ")) / 0

except (ValueError, ZeroDivisionError):
    # Handle multiple exceptions
    print("Invalid input or division by zero!")

Raise Exception:

We can explicitly raise exceptions using the raise statement:

Example:

x = -1
if x < 0:
    raise ValueError("x cannot be negative")

Custom Exceptions:

We can define custom exception classes by inheriting from the Exception class or one of its subclasses:

Example:

class YourCustomError(Exception):
    pass

try:
    raise YourCustomError("An error occurred")
except YourCustomError as e:
    print(e)

Exception Propagation:

Exceptions propagate up the call stack until they are caught by an appropriate except block.

If an exception is not caught, the program terminates and prints a traceback.

Exception Hierarchy:

Python has a rich hierarchy of built-in exception types.

Some common built-in exceptions include TypeError, ValueError, ZeroDivisionError, IndexError, KeyError, and IOError, among others.

Handling Errors Gracefully:

The primary goal of exception handling is to gracefully handle errors and ensure that the program does not crash unexpectedly.

This may involve logging the error, providing informative error messages to the user, or attempting to recover from the error and continue execution.

Example:

try:
    # Code that may raise an exception
    data = open("nonexistent_file.txt", "r")

except FileNotFoundError:
    # Handle the specific exception
    print("Error: File not found!")

Note:

Exception handling is an essential aspect of writing robust and reliable Python code.

It allows us to anticipate and handle potential errors, making our programs more resilient in the face of unexpected conditions.

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