Throw custom exception in Python with input parameters to print

Question

I have seen a few examples like this , this and this , which show how to throw custom exception in Python. But what I'm hoping to accomplish is something like this:

## in main.py
import my_errors

if  os.path.exists(filename):
    # here, I'd like to pass in 'filename' as parameter to FileNotFound
    raise my_errors.FileNotFound(filename)

## in my_errors.py
class MyError(Exception):
    pass

class FileNotFound(MyError):
    # here, how do I make this FileNotFound class to accept/receive 'filename' as parameter so that I can print something informative like below
    print("FileNotFound ERROR: Please make sure that the following file exists:", filename)

Thank you in advance for your help!

Answer 1

You'll want to implement your own __init__() function.

class FileNotFound(MyError):

    def __init__(self, filename):
        super().__init__("FileNotFound ERROR: Please make sure that the following file exists:" % filename)

Note that this will set the error message of the exception. To print normally:

class FileNotFound(MyError):

    def __init__(self, filename):
        print("FileNotFound ERROR: Please make sure that the following file exists:", filename)

        super().__init__(filename)