error and exception handling

• In Python, errors and exceptions are mechanisms to handle unexpected situations that arise during program execution.
• They help prevent your program from crashing abruptly and offer ways to recover gracefully or provide meaningful feedback to the user.
• Types of Errors
  • Syntax Errors: These are violations of Python's grammar rules, like typos or missing colons. These are detected before the program even runs.
  • Exceptions: These are runtime errors that occur during program execution. They can be caused by various factors like division by zero, accessing non-existent elements, or file-related issues.
• Exception Handling with try-except
  • The primary mechanism for handling exceptions in Python is the try-except block

try:
    # Code that might raise an exception
    result = 10 / 0  # This will cause a ZeroDivisionError exception
    print(result)
except ZeroDivisionError:
    print("Oops! You cannot divide by zero.")

try: # Code that might raise an exception result = 10 / 0 # This will cause a ZeroDivisionError exception print(result) except ZeroDivisionError: print("Oops! You cannot divide by zero.")

• Explanation

  • try:: This block contains the code that might raise an exception.
  • except ZeroDivisionError:: This except block handles the ZeroDivisionError exception specifically. If any code within the try block raises this exception, the code within this except block will execute instead.
  • You can have multiple except blocks to handle different types of exceptions.

• else Clause

  • The else clause (optional) is used when no exception occurs within the try block. The code within the else block executes only if the try block completes successfully without raising an exception.

try:
    result = 10 / 5
    print(result)
except ZeroDivisionError:
    print("Oops! You cannot divide by zero.")
else:
    print("The division operation was successful.")

try: result = 10 / 5 print(result) except ZeroDivisionError: print("Oops! You cannot divide by zero.") else: print("The division operation was successful.")

• finally Clause
  • The finally clause (optional) executes regardless of whether an exception occurs or not. It's commonly used to release resources or perform cleanup tasks.

try:
    file = open("myfile.txt", "r")  # Open a file
    data = file.read()
finally:
    if file:
        file.close()  # Close the file even if an exception occurs

try: file = open("myfile.txt", "r") # Open a file data = file.read() finally: if file: file.close() # Close the file even if an exception occurs

• Common Exceptions
  • ZeroDivisionError: Attempting to divide by zero.
  • IndexError: Trying to access an element at an invalid index (out of bounds).
  • NameError: Referencing a variable that hasn't been defined.
  • KeyError: Trying to access a key that doesn't exist in a dictionary.
  • FileNotFoundError: Attempting to open a file that doesn't exist.
• Raising Exceptions
  • You can intentionally raise exceptions using the raise statement. This is useful for signaling errors from within your code.

def validate_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative.")

validate_age(-5)  # This will raise a ValueError

def validate_age(age): if age < 0: raise ValueError("Age cannot be negative.") validate_age(-5) # This will raise a ValueError

• Key Points
  • Use exception handling (try-except) to handle unexpected errors gracefully and prevent program crashes.
  • Employ specific except blocks to handle different exception types.
  • The else clause executes only if no exception occurs in the try block.
  • The finally clause is always executed, regardless of exceptions.
  • Understand common exceptions to anticipate potential errors in your code.