How to Handle Exceptions In Python?

When writing code in Python, it is important to handle exceptions to prevent the program from crashing when unexpected errors occur.

You can use try-except blocks to catch and handle exceptions in Python. The try block contains the code that may raise an exception, while the except block specifies what action to take if an exception is raised.

You can also use multiple except blocks to handle different types of exceptions separately. This allows you to provide specific error messages or perform different actions based on the type of exception that occurred.

Additionally, you can use the else block to execute code that should only run if no exceptions were raised in the try block, and the finally block to clean up resources or perform final actions regardless of whether or not an exception was raised.

Overall, handling exceptions in Python allows you to gracefully handle errors and prevent your program from crashing unexpectedly.

How to create custom exception classes in Python?

To create a custom exception class in Python, you can follow these steps:

1. Create a new class that inherits from the built-in Exception class or a subclass of Exception that suits your needs.
2. Add an __init__ method to the class to initialize the exception with any necessary arguments.
3. Optionally, you can add custom methods or properties to the class to provide additional functionality.
4. You can also override the __str__ method to define a custom string representation of the exception.

Here's an example of creating a custom exception class in Python:

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class CustomException(Exception):
    def __init__(self, message, custom_data=None):
        self.message = message
        self.custom_data = custom_data

    def __str__(self):
        return f'{self.message} - Custom Data: {self.custom_data}'

# Example Usage
try:
    raise CustomException("An error occurred", custom_data={"reason": "Some reason"})
except CustomException as e:
    print(e)

In this example, we created a custom exception class CustomException that takes a message and optional custom data as arguments in the __init__ method. We also defined a custom string representation for the exception using the __str__ method.

When raising the custom exception, you can pass the message and custom data as arguments. When catching the exception, you can access the message and custom data using the exception object.

How to catch specific exceptions in Python?

To catch specific exceptions in Python, you can use the try and except blocks.

Here is an example of how to catch a specific exception (in this case, a ValueError):

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try:
    x = int("hello")
except ValueError:
    print("Oops! That was not a valid number.")

In this code snippet, the try block attempts to convert the string "hello" to an integer, which will raise a ValueError. The except block catches the ValueError and prints a message.

You can catch multiple specific exceptions in the same try block by using multiple except blocks like this:

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try:
    x = int("hello")
except ValueError:
    print("Oops! That was not a valid number.")
except TypeError:
    print("Oops! Type error occurred.")

You can also catch all exceptions (including specific ones) by not specifying any exception type in the except block:

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try:
    x = int("hello")
except ValueError:
    print("Oops! That was not a valid number.")
except:
    print("An error occurred.")

It is generally recommended to catch specific exceptions rather than catching all exceptions, as it allows you to handle different types of errors in a more controlled way.

What is the meaning of the else block in Python exception handling?

In Python exception handling, the else block is used to specify a block of code that should be executed if the try block does not raise any exceptions. It is optional and follows the try block and any except blocks. The code in the else block will only be executed if no exceptions are raised in the try block. It is often used to execute code that should only run if the try block succeeds.

What is the role of the sys module in Python exception handling?

The sys module in Python exception handling provides access to some variables used or maintained by the interpreter and to functions that interact closely with the interpreter.

Some of the functions related to exception handling in the sys module include:

1. sys.exc_info(): This function returns a tuple of three values that give information about the current exception being handled.
2. sys.exc_clear(): This function clears the current exception information.
3. sys.last_type, sys.last_value, sys.last_traceback: These variables store information about the last exception that occurred.

By using the functions and variables provided by the sys module, developers can customize their exception handling logic and obtain more information about exceptions that occur in their Python programs.