def addRawHeader(self, name, value):
        """
        Add a new raw value for the given header.

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

        @type value: L{bytes} or L{unicode}
        @param value: The value to set for the named header.
        """
        values = self.getRawHeaders(name)

        if values is not None:
            values.append(value)
        else:
            values = [value]

        self.setRawHeaders(name, values)

        Add a new raw value for the given header.

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

        @type value: L{bytes} or L{unicode}
        @param value: The value to set for the named header.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/http_headers.py