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Exception Hierarchy

Exception Hierarchy in Python for Programmers

Exception handling is an important concept in programming languages, which allows programs to handle errors gracefully during execution. Python provides a robust exception hierarchy that allows programmers to create custom exceptions and handle them accordingly. Exceptions can be handled using the try/except statements, and this guide will provide an overview of the Python exception hierarchy with examples and tips.

Base Exception

The base of the exception hierarchy is the BaseException class, which is the root of the exception tree. All the exceptions defined in Python are derived from this class. All exceptions should inherit from this class, either directly or indirectly.

Example 1: Custom Exception

To create a custom exception, simply create a class that derives from the BaseException class. The following example creates a custom exception called MyCustomException and raises it if the user input is invalid:

class MyCustomException(BaseException):
    pass

def check_input(value):
    if not value.isalpha():
        raise MyCustomException("Input is invalid")

Standard Exceptions

Python also provides a set of standard exception classes that are derived from the BaseException class. These exceptions are defined in the exceptions module, and include the following:

  • Exception
  • LookupError
  • ImportError
  • KeyError
  • IndexError
  • NameError
  • ValueError
  • RuntimeError
  • TypeError

These exceptions can be used to handle errors in a more specific way, as they provide more information about the cause of the error. For example, the ValueError exception is raised when a function receives an argument of the wrong type.

Example 2: Handling Multiple Exceptions

The try/except statement allows multiple exceptions to be handled in the same block of code. The following example handles the ValueError and TypeError exceptions:

try:
    value = int(input("Enter a number: "))
except (ValueError, TypeError) as err:
    print(err)

Tips

  • When creating custom exceptions, it’s best to use the BaseException class as the base class.
  • Standard exceptions should be used to handle errors in a more specific way.
  • Multiple exceptions can be handled in the same try/except block.

Example 3: Catching All Exceptions

The try/except statement can also be used to catch all exceptions. This is useful for debugging, as it allows you to handle any errors that may occur without having to specify each one individually. The following example catches all exceptions:

try:
    value = int(input("Enter a number: "))
except:
    print("An error occurred")

By using the Python exception hierarchy, programmers can create custom exceptions and handle them accordingly. This guide has provided an overview of the Python exception hierarchy with examples and tips.