Should I raise ValueError or OSError for non-existent file arguments?

Question

When a program receives a filename argument that does not exist, or is not a directory, I want to raise an error. But what error is considered best practice?

I understand that ValueError is often used to signal invalid arguments (and I've seen several questions about it). I also understand that, especially after the reorganization of exceptions in Python 3.3 ( PEP 3151 ), OSError is the catch-all category for problems related to interaction with the system.

So, I have a program that expects a filename argument. If the name supplied by the caller does not exist, or exists but is a directory, what error should I raise? It's an incorrect argument so it seems that ValueError applies; but if I try to read from it as a file, I will get an OSError -- so shouldn't this be returned for consistency?

Answer 1

does it really matter?(I assume you are not catching this exception and it is purely for informational purposes of an individual looking at the terminal output) none of that will be seen by the operating system as such I would just

raise Exception("Invalid Arguments, expected a file that exists not %r"%(filename))

or just let it fail when it tries to open the file naturally even