title: Propagating c++ exception to cython - python exception
body: <p>I have a problem with Cython 0.17.1</p>
  
  <p>My function throws a <code>std::runtime_error</code> if a file doesn't exist, I'd like to propagate this exception in some manner to my Cython code.</p>
  
  <pre><code>void loadFile(const string &amp;filename)
  {
      // some code, if filename doesn't exists 
      throw std::runtime_error( std::string("File doesn't exists" ) );
  }
  </code></pre>
  
  <p>and from Cython after the right wrapping of the function:</p>
  
  <pre><code>try:
      loadFile(myfilename)
  except RuntimeError:
      print "Can't load file"
  </code></pre>
  
  <p>but this exception is always ignored, how can I catch c++ exceptions from Python?</p>