Raising custom exceptions in python
With the presence of custom exceptions in Python programming, you can define and indicate specific error conditions in the program code in your existing file handling, in these custom exception methods you will be able to control and manage any type of exceptions occurring in the program. Many times we want to manage and display error message information through some programming logic in some special conditions. Python programs can be better customized and modified with custom exceptions. And any error displayed in the program can be better displayed and controlled or managed.
So let’s display and manage custom exceptions in Python programs.
Defining custom exceptions in Python programs.
To define custom exceptions in Python programs based on your needs, you have to create a new class program. Which is found in the built-in exception class of the Python program or any of its subclass inherit properties.
Custom exception example in Python program.
class generateerror(Exception):
def __init__(me, information):
me.information = information
super().__init__(me.information)
In the above program example.
generateerror is a custom exception class that inherits from the built-in exception class of Python program.
Here the __init__ method is used to accept the information parameter, which gives you access to define a custom error information message when raising this exception.
Raising a custom exception in Python program.
Once you define a custom exception in Python program, you can raise the exception using the raise statement wherever needed in your program code.
def manipulate_file(file_location):
if not file_path.endswith(‘.txt’):
raise CustomError(f”Invalid file mode – ‘{file_location}’ let use .txt file extension.”)
try:
with open(file_location, ‘r’) as file: # open and close file in read mode
# let start process file from here
pass
except FileNotFoundError:
raise CustomError(f” the search file ‘{file_location}’ not get. checkout the proper file location”) # raise custom exception error
except IOError as e:
raise CustomError(f” file io disk error ‘{file_location}’: {e}”)
In the above program example.
The manipulate_file user defined function checks whether file_location is proper with .txt extension. If not proper txt file, it displays CustomError exception message along with a specific program error message.
Where inside the try catch block, standard file I/O operations are executed.
Where specific exceptions (FileNotFoundError, IOError) are caught or handled, and re-raised as CustomError instances with a customized program error message.
Handling Custom Exceptions in Python Programs.
To manage custom exceptions in any Python program, you can use the try-except error handling block method in the main source code of your existing program or in any program function that calls the program code that raises the custom exception in your existing program.
file_location = ‘sample.dat’
try:
manipulate_file(file_location)
except CustomError as e:
print(f”Error – Custom Error generated – {e.message}”)
Here, manipulate_file(file_location) is called inside the try block.
If a CustomError (or any of its subclasses) is raised during the execution of manipulate_file, you can find or handle it using an except block, and a custom error message (e.message) is printed in the program.
Benefits of using custom exceptions in Python programs.
Program code clarity and readability – Custom program exceptions provide clear indication of specific error conditions in any file handling, making your program code easier to understand and maintain.
Easy program error management flexibility – Allows you to manage different error sequences in your program with specific actions or messages corresponding to each condition.
Layered error management – Enables layered program error management, where specific exceptions can be caught and processed at particular levels of your application.
Python custom exception best practices.
Use descriptive names in try except – Select the correct name for your custom exception to clearly communicate the nature of the error in file handling.
Provide informative error messages – Display detailed error messages for your custom exceptions to aid in debugging and troubleshooting a program in Python file handling.
Document custom exceptions programmatically – Properly document custom exceptions in your existing program codebase. This includes how and when to raise program exceptions through documentation in your program. Program documentation also provides proper support to any programmer or developer who maintains or extends the program source code in the future.
