def setHeader(k, v):
        """
        Set an HTTP response header.  Overrides any previously set values for
        this header.

        @type k: L{bytes} or L{str}
        @param k: The name of the header for which to set the value.

        @type v: L{bytes} or L{str}
        @param v: The value to set for the named header. A L{str} will be
            UTF-8 encoded, which may not interoperable with other
            implementations. Avoid passing non-ASCII characters if possible.
        """

        Set an HTTP response header.  Overrides any previously set values for
        this header.

        @type k: L{bytes} or L{str}
        @param k: The name of the header for which to set the value.

        @type v: L{bytes} or L{str}
        @param v: The value to set for the named header. A L{str} will be
            UTF-8 encoded, which may not interoperable with other
            implementations. Avoid passing non-ASCII characters if possible.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/iweb.py