def __str__(self) -> str:
        """Returns formatted headers suitable for HTTP transmission."""
        strs = []
        for key, value in self.to_wsgi_list():
            strs.append(f"{key}: {value}")
        strs.append("\r\n")
        return "\r\n".join(strs)
Returns formatted headers suitable for HTTP transmission.
src/werkzeug/datastructures/headers.py