def retry_after(self) -> datetime | None:
        """The Retry-After response-header field can be used with a
        503 (Service Unavailable) response to indicate how long the
        service is expected to be unavailable to the requesting client.

        Time in seconds until expiration or date.

        .. versionchanged:: 2.0
            The datetime object is timezone-aware.
        """
        value = self.headers.get("retry-after")
        if value is None:
            return None

        try:
            seconds = int(value)
        except ValueError:
            return parse_date(value)

        return datetime.now(timezone.utc) + timedelta(seconds=seconds)
The Retry-After response-header field can be used with a
        503 (Service Unavailable) response to indicate how long the
        service is expected to be unavailable to the requesting client.

        Time in seconds until expiration or date.

        .. versionchanged:: 2.0
            The datetime object is timezone-aware.
        
src/werkzeug/sansio/response.py