9. Exception Handling in Python

Página 48

Exception handling in Python is a crucial part of any robust and secure program. Exceptions are events that occur during the execution of a program that interrupt the normal flow of the program. In Python, exceptions are raised when some internal errors occur. Python has many built-in exceptions like IOError, ValueError, ZeroDivisionError, ImportError, NameError, TypeError etc.

Exceptions in Python are not necessarily fatal errors; rather, they are extraordinary events that need to be dealt with effectively to avoid abrupt program closure. Python provides an exception handling framework to handle these anomalies and ensure that the program can continue with execution or terminate gracefully.

Exception handling in Python is accomplished using a four-component structure: try, except, else and finally.

The try block is used to wrap code that could potentially cause an exception. The code block inside the try block executes normally. If an exception occurs, execution of the try block is stopped and control is passed to the except block.

try:
    # code that might raise an exception
except ExceptionType:
    # code that will be executed if the exception occurs

The except block is where we define how the program should respond to the exception. We can specify different exception blocks to handle different types of exceptions. If the exception type mentioned after except matches the exception that occurred in the try block, then that except block is executed.

try:
    # code that might raise an exception
except ZeroDivisionError:
    # code that will be executed if the ZeroDivisionError exception occurs
except IndexError:
    # code that will be executed if the IndexError exception occurs

The else block in Python is optional. The code inside the else block is executed if no exception occurs in the try block.

try:
    # code that might raise an exception
except ZeroDivisionError:
    # code that will be executed if the ZeroDivisionError exception occurs
else:
    # code that will be executed if no exception occurs

The finally block is also optional. The code inside the finally block runs whether or not an exception has occurred. This is useful for cleanup actions such as closing files or network connections.

try:
    # code that might raise an exception
except ZeroDivisionError:
    # code that will be executed if the ZeroDivisionError exception occurs
finally:
    # code that will be executed regardless of whether an exception occurs or not

In addition to built-in exceptions, Python allows programmers to define their own custom exceptions by creating a new exception class. These custom exceptions can then be raised using the raise statement.

class CustomError(Exception):
    pass

try:
    raise CustomError
except CustomError:
    print("A custom exception occurred.")

In summary, exception handling is an important part of software development in Python. It allows programmers to handle errors and exceptions cleanly and efficiently without interrupting program execution. By properly understanding and using Python's exception-handling framework, you can write safer, more robust, and more maintainable code.

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4910. Python modules and packages