How to remove the "Traceback most recent call last" in Python when raising an exception?

Question

I am creating a Python program that requires the use of the OS module, and I would like to custom-report error messages. I am using try and except to accomplish this:

try:
    os.mkdir(name)
except FileExistsError:
    raise FileExistsError(name + "\n" + "                        ^ The directory you specified already exists.")

But, I would like to remove the

Traceback (most recent call last):
  File "file.py", line 20, in <module>
    raise FileExistsError(name + "\n" + "                        ^ The directory you specified already exists.")

part so that the code that raises this exception is not printed every time that I raise the exception.

How would I go about doing this?

Answer 1

How most command line programs do it is to catch the exception near the top of the program where you interact with the user and print it out in a form that is useful to them:

def makedir(name):
    try:
        os.mkdir(name)
    except FileExistsError:
        raise FileExistsError(
            name + "\n" + "^ The directory you specified already exists."
        )


def main():
    try:
        makedir("/tmp")
    except FileExistsError as e:
        print("OOOPS", e)
        return

If you catch too broad of an exception class at the top, you will harm your own ability to debug and your user's ability to give you precise error messages, so you should be precise. In fact you might want to invent your own exception classes like this:

class MyAppExceptions(Exception):
    pass


class MyAppFileExists(MyAppExceptions):
    pass


def makedir(name):
    try:
        os.mkdir(name)
    except FileExistsError:
        raise MyAppFileExists(
            name + "\n" + "^ The directory you specified already exists."
        )


def main():
    try:
        makedir("/tmp")
    except MyAppFileExists as e:
        print("OOOPS", e)
        return

Then if your program gets a FileExistsError for a reason that you did not anticipate, you will still get an exception traceback that you can use for debugging.