title: Raising builtin exception with default message in python
body: <p>I'm trying to implement a method that returns an error whenever a certain directory does not exist. </p>
  
  <p>Rather than doing <code>raise OSError("Directory does not exist.")</code>, however, I want to use the builtint error message from OSError: <code>OSError: [Errno 2] No such file or directory:</code>. 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 <code>raise</code>).</p>
  
  <p>Any pointers? (other than manually doing <code>OSError("[Errno 2] No such file or directory: ")</code>)</p>