code: def OpenFile(self, filename):
      
      (mime_type, encoding) = mimetypes.guess_type(filename)
      assert mime_type
      # A crude guess of when we should use binary mode. Without it non-unix
      # platforms may corrupt binary files.
      if mime_type.startswith('text/'):
        mode = 'r'
      else:
        mode = 'rb'
      return open(os.path.join(self.server.file_dir, filename), mode), mime_type
docs: Try to open filename in the static files directory of this server.
      Return a tuple (file object, string mime_type) or raise an exception.