How Can I Manually Raise Exceptions in Python and Handle Them Effectively?

Manually Raising Exceptions in Python

Purpose

Raising exceptions allows for controlled handling of errors and interruptions in Python code. This article demonstrates how to manually raise specific exceptions, allowing them to be caught and handled appropriately.

Raising Exceptions

To raise an exception, use the raise keyword followed by the exception class and any custom message arguments. For example:

raise ValueError('Invalid input value.')

Best Practices for Raising Exceptions

Choose a Specific Exception Class:
Use the most specific Exception constructor that fits the situation, as generic exceptions can hide bugs and prevent specific handling.

Include a Descriptive Message:
Provide a specific and meaningful error message to help diagnose the issue.

Avoid Modifying Exceptions:
If you need to modify the exception, use sys.exc_info() to preserve the stack trace. However, this is generally not recommended and can introduce compatibility issues between Python 2 and 3.

Best Practices for Exception Handling

Use the except Clause:
When handling exceptions, use the except clause to catch specific exception types.

Bare raise for Re-Raising:
To re-raise an exception while preserving the stack trace, use a bare raise statement:

try:
    # Code that may raise an exception
except SpecificException:
    logger.error(error)
    raise

Deprecated Methods

Avoid these methods for raising exceptions:

• raise ExceptionType, 'message': Deprecated in Python 3.
• raise 'message': Invalid in all modern Python versions.

Example Usage

def check_input(value):
    if not isinstance(value, int):
        raise TypeError('Input must be an integer.')
    if value < 0:
        raise ValueError('Input must be positive.')

try:
    check_input(-1)
except TypeError as error:
    print('Wrong input type:', error)
except ValueError as error:
    print('Invalid input value:', error)

Custom Error Types

Create custom error types to handle specific scenarios:

class MyCustomError(Exception):
    '''This error represents a specific problem with my code.'''

Usage:

raise MyCustomError('An unexpected issue occurred.')
except MyCustomError as error:
    print('Custom error raised:', error)

The above is the detailed content of How Can I Manually Raise Exceptions in Python and Handle Them Effectively?. For more information, please follow other related articles on the PHP Chinese website!