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Python Try, except blocks

 try and except blocks in Python are used for handling exceptions (errors) that may occur during the execution of a program. This allows you to manage errors gracefully without stopping the entire program. Here's a detailed explanation and some examples:

Basic Structure

The basic structure of a try and except block looks like this:

try: # Code that might raise an exception risky_operation() except ExceptionType: # Code to handle the exception handle_exception()


Example: Handling a Division by Zero

Let's look at an example where we handle a ZeroDivisionError

try: result = 10 / 0 except ZeroDivisionError: print("Error: Division by zero is not allowed.")


Catching Multiple Exceptions

You can catch multiple exceptions by specifying multiple except blocks:

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Error: Division by zero is not allowed.")
except TypeError:
    print("Error: Invalid type used for division.")

Catching All Exceptions

To catch any exception, you can use a generic except block without specifying an exception type. However, this is generally not recommended because it can make debugging more difficult:

try: result = 10 / 0 except: print("An error occurred.")


Using the else Block

An else block can be used to specify code that should be executed if no exceptions are raised:

try: result = 10 / 2 except ZeroDivisionError: print("Error: Division by zero is not allowed.") else: print(f"Result is {result}")


Using the finally Block

A finally block can be used to specify code that should be executed no matter what, whether an exception was raised or not:

try: result = 10 / 0 except ZeroDivisionError: print("Error: Division by zero is not allowed.") finally: print("This block will always execute.")


Raising Exceptions

You can raise exceptions using the raise statement. This can be useful for handling certain error conditions explicitly:

def check_positive(number): if number < 0: raise ValueError("Number must be positive") try: check_positive(-1) except ValueError as e: print(e)


Full Example: File Operations

Here’s a more comprehensive example that demonstrates reading from a file with error handling:

try: with open('example.txt', 'r') as file: contents = file.read() except FileNotFoundError: print("Error: File not found.") except IOError: print("Error: An I/O error occurred.") else: print(contents) finally: print("Finished file operation.")


Custom Exception Classes

You can define your own exception classes by inheriting from the Exception class:

class CustomError(Exception): pass def risky_operation(): raise CustomError("Something went wrong!") try: risky_operation() except CustomError as e: print(e)


Summary

  • try block: Contains code that might raise an exception.
  • except block: Contains code to handle the exception.
  • else block: Contains code to be executed if no exceptions are raised.
  • finally block: Contains code to be executed no matter what.

Using these blocks effectively allows you to manage errors gracefully, ensuring that your program can handle unexpected situations without crashing.


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