Save the object to file given by filename.

def save(self, filename, format=None, **kwargs):
        """ Save the object to file given by filename.
        """
        if format is None:
            # try to derive protocol from file extension
            format = format_from_extension(filename)
        with file(filename, 'wb') as fp:
            self.save_to_file_object(fp, format, **kwargs)