Python raise NotADirectoryError

Question

I'm trying to raise an error when a directory does not exist, before I open files in that directory. According to this response I should use the most specific Exception constructor for my issue, which I think is NotADirectoryError. But running the code below I get NameError: global name 'NotADirectoryError' is not defined. Thanks in advance for any help!

import os
if not os.path.isdir(baselineDir):
  raise NotADirectoryError("No results directory for baseline.")

And if there's a better way to do this please suggest it, thanks.

Answer 1

You're likely using Python 2, which does not define NotADirectoryError. However, this is defined in Python 3, for exactly the purpose you're trying to use it for.

If you need to use Python 2, you'll need to define the error yourself through a class. Read through the docs about user-defined exceptions to learn about subclassing the Exception class and customizing it for your own needs, if necessary. Here's a very simple example:

class NotADirectoryError(Exception):
    pass

This will take the string passed to it and print it out, just like you want.