[FIXED] What does [Errno 2] mean in python?

Issue

I was playing around with python, and I was trying to open a file. I accidentally made a typo, and got the expected error:

FileNotFoundError: [Errno 2] No such file or directory: 'tlesting.py'

It was supposed to be testing.py if you are wondering.

Of course, I expected the error, but I want to know the reason behind why [Errno 2] is included. I got curious, so I tried raising the error myself: raise FileNotFoundError("This is a test"), and got an output of: FileNotFoundError: This is a test, but no [Errno 2] anymore. Is this something to do with the current version of python or my current operating system?

Solution

To add the [Errno 2] tag, you can pass the appropriate error number as an explicit first argument:

>>> import errno
>>> raise FileNotFoundError("foo")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileNotFoundError: foo
>>> raise FileNotFoundError(errno.ENOENT, "foo")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileNotFoundError: [Errno 2] foo

Answered By - chepner