Adventures in Machine Learning

Exceptional Python: Resolving TypeError Through Custom Exception Classes

Understanding TypeError: Exceptions Must Derive from BaseException

Programming languages rely heavily on exceptions to inform developers when something unexpected happens in their code. An exception is an error that occurs during runtime, causing the program to halt.

In Python, exceptions must derive from the BaseException class. Failing to follow this rule results in a TypeError.

This article provides insights into the causes and resolution of the TypeError.

Causes of the TypeError

The raise keyword in Python is used to trigger an exception. However, when you use a string instead of a class derived from BaseException, you get a TypeError.

For example, the code below would raise a TypeError:

raise "Invalid input"

When an error occurs in a program, the interpreter generates an error message to help pinpoint the issue. However, if the error message is not derived from BaseException, the interpreter crashes, and you get a TypeError.

Resolving the TypeError

When dealing with exceptions in Python, you have two options. You can use built-in exception classes or create your own custom exception class.

The built-in exception classes include AssertionError, ValueError, RuntimeError, and many others. These classes are derived from the Exception class, which, in turn, is derived from the BaseException class.

If you decide to create your own custom exception class, you must ensure that it derives from the Exception class. The Exception class provides a robust set of methods that you can customize to suit your needs.

When defining your custom exception class, remember to add a suitable error message that describes the issue. For instance, suppose you want to create a custom exception class named MyException.

Here’s an example of how to define the class:

class MyException(Exception):
  def __init__(self, message):
    self.message = message

Also, ensure that your traceback includes the location of the code that triggered the exception.

Best Practices for Creating Custom Exception Classes

Why Use the Exception Class Instead of BaseException Class?

When creating a custom exception class, it is essential to know the differences between the Exception class and the BaseException class.

Using the Exception class is recommended over BaseException because it provides additional functionality to handle exceptions. The Exception class provides a traceback object, which you can use to trace the error from the point it occurred back to the code’s origin.

When using BaseException, you risk interrupting the normal functioning of the interpreter. For instance, suppose you have a try-except block in your code and catch an error derived from BaseException.

In that case, it will stop the program, including interrupting the handling of the SystemExit exception.

Recommendations for Creating Custom Exception Classes

  1. Use the Exception class as a superclass when defining your custom exception class.
  2. Define error messages that describe the issue and help the user to troubleshoot the problem.
  3. Namespacing your exceptions could help keep the code organized, making it easier to debug and maintain.
  4. Add an error code to the exception class to help customers identify the issue.


Exceptions are an essential part of Python programming. Understanding how exceptions work, their various causes, and resolutions is crucial for building more robust and maintainable code.

In summary, you can avoid raising the TypeError by ensuring that any exceptions you raise derive from BaseException. Additionally, when creating custom exception classes, it is recommended to use the Exception class as the superclass and define clear error messages.

Finally, namespacing and error codes help keep your exceptions organized and enable customers to identify the issue. Exception handling in Python can be a critical part of writing a robust and maintainable codebase.

Understanding how to handle exceptions through either built-in exception classes or custom exception classes is essential to producing code that functions correctly. This article has covered some of the primary causes of the TypeError message, as well as solutions to resolve the issue.

It has also discussed best practices concerning custom exception classes for Python. We will now explore these topics in more detail, adding 1000 words of content to the article.

Fixing the TypeError

TypeError occurs in situations where developers have tried to raise an error with a string value. One common place where this mistake manifests is during input validation.

Essentially, if you raise an error with a string message, the TypeError raises because the error should come from an Exception object.

Here’s an example to demonstrate how input validation can raise a TypeError:

def validate_input(input_value):
    if not input_value.isdigit():
        raise TypeError('Invalid input')

If this code is executed, the interpreter will raise a TypeError because the message would not have been raised from an Exception object.

One way of fixing this is to define classes that inherit from exception. For example, ValueError is one of the built-in exceptions that inherit from Exception:

def validate_input(input_value):
    if not input_value.isdigit():
        raise ValueError('Invalid input')

Here, changing the type of error raised to ValueError fixes the TypeError issue.

In general, when defining custom exceptions, ensuring that those classes inherit from the built-in Exception class prevents the occurrence of TypeError messages due to using string objects.

Best Practices for Creating Custom Exception Classes

When it comes to handling exceptions through the use of custom exception classes, it’s helpful to adopt some form of consistent naming conventions that make it easier for other developers to understand why exceptions arise, as it improves readability and maintainability of code. Namespacing your exception classes can be especially beneficial in these scenarios, leading to cleaner and more organized code.

class DatabaseException(Exception):
class ConnectionException(DatabaseException):
class QueryException(DatabaseException):

This can allow developers to easily identify the type of exception thrown and understand how these exceptions are related. Furthermore, when an error message is added with the exception, the error is more informative and precise.

Similarly, assigning error codes to exception classes can also be a helpful way of identifying specific issues with the codebase quickly. When an end-user encounters an error, having an error code can indicate a specific location in the code where the problem arose.

Consider the following example:

class Error(Exception):
    """Base class for exceptions."""
class ValidationFailed(Error):
    """Raised when validation fails."""
    code = 1001
class InputError(ValidationFailed):
    """Raised when the input is incorrect."""
    code = 1002
class ServerError(Error):
    """Raised when a server error occurs."""
    code = 2001

The “code” attribute added to each of these classes more finely tunes the error, allowing developers and users to troubleshoot and fix the issue in less time, leading to a more efficient and effective development process. When choosing to use custom exception classes, it is essential to adhere to established rules and conventions.

In general, the best practice is to have exception classes inherit from the Exception class instead of the BaseException class. This is because doing so can avoid problems such as interrupting the handling of SystemExit exceptions when using BaseException.

Using the Exception Class Instead of BaseException

When creating a custom exception class, by default, developers may want to extend the BaseException class, considering that it is the ultimate base class for all exceptions built into Python. However, when caught in the Global scope, BaseException can catastrophically interrupt Python’s execution.

Fortunately, Python provides the Exception class, which is the parent class of all built-in exceptions and has a better-specified behavior than BaseException. To demonstrate, consider the following example:

except BaseException as e:

When run, this code will abruptly exit the Python interpreter.

However, when you use the Exception class instead of the BaseException class, the try-except block can function ordinarily without interrupting Python’s regular function. python

except Exception as e:

The code above will return the normal exceptions that would arise in Python when calling an exit() function, without the risk of unwanted behavior.

In conclusion, it is considered best practice to use built-in exceptions or custom Exception classes instead of BaseException to avoid unwanted interruptions in Python’s execution. In addition, appropriately structuring your custom exception classes for your particular development environment (i.e., providing error messages and codes, among other things), will lead to better readability, maintainability, and overall better code quality.

In summary, proper exceptions handling is a crucial aspect of producing a maintainable and robust codebase in Python. Understanding how to resolve the TypeError by utilizing built-in exception classes or custom exception classes derived from the Exception class, is critical to avoid interrupting Python’s regular function and enhancing the end-user experience.

Best practices for creating custom exception classes include using namespacing and error codes, in addition to adding robust error messages that aid in troubleshooting. By following these best practices, developers can write more readable and organized code that is easier to maintain and troubleshoot.

The key takeaway from this article is to ensure that any exceptions raised in Python should inherit from the Exception class and to properly structure custom exception classes to improve readability for developers and end-users.

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