Raising builtin exception with default message in python

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') 

Answer 2

To get the error message for a given error code, you might want to use os.strerror:

>>> os.strerror(2) 'No such file or directory' 

Also, you might want to use errno module to use the standard abbreviations for those errors:

>>> errno.ENOENT 2 >>> os.strerror(errno.ENOENT) 'No such file or directory'