Question

I’m trying to implement a method that returns an error whenever a certain directory does not exist.

Rather than doing raise OSError("Directory does not exist."), however, I want to use the builtint error message from OSError: OSError: [Errno 2] No such file or directory:. This is because I am raising the exception in the beginning of the method call, rather than later (which would invoke the same message from python, without any necessary raise).

Any pointers? (other than manually doing OSError("[Errno 2] No such file or directory: "))

Answer 1

import os

try:
    open('foo')
except IOError as err:
    print(err)
    print(err.args)
    print(err.filename)    

produces

[Errno 2] No such file or directory: 'foo'
(2, 'No such file or directory')
foo

So, to generate an OSError with a similar message use

raise OSError(2, 'No such file or directory', 'foo')