How to use the parsel.utils.flatten function in parsel

def re(self, regex, replace_entities=True):
        """
        Call the ``.re()`` method for each element in this list and return
        their results flattened, as a list of unicode strings.

        By default, character entity references are replaced by their
        corresponding character (except for ``&`` and ``<``.
        Passing ``replace_entities`` as ``False`` switches off these
        replacements.
        """
        return flatten([x.re(regex, replace_entities=replace_entities) for x in self])

Call the ``.xpath()`` method for each element in this list and return
        their results flattened as another :class:`SelectorList`.

        ``query`` is the same argument as the one in :meth:`Selector.xpath`

        ``namespaces`` is an optional ``prefix: namespace-uri`` mapping (dict)
        for additional prefixes to those registered with ``register_namespace(prefix, uri)``.
        Contrary to ``register_namespace()``, these prefixes are not
        saved for future calls.

        Any additional named arguments can be used to pass values for XPath
        variables in the XPath expression, e.g.::

            selector.xpath('//a[href=$url]', url="http://www.example.com")
        """
        return self.__class__(flatten([x.xpath(xpath, namespaces=namespaces, **kwargs) for x in self]))

def css(self, query):
        """
        Call the ``.css()`` method for each element in this list and return
        their results flattened as another :class:`SelectorList`.

        ``query`` is the same argument as the one in :meth:`Selector.css`
        """
        return self.__class__(flatten([x.css(query) for x in self]))