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

def re_first(self, regex, default=None, replace_entities=True):
        """
        Call the ``.re()`` method for the first element in this list and
        return the result in an unicode string. If the list is empty or the
        regex doesn't match anything, return the default value (``None`` if
        the argument is not provided).

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

def re_first(self, regex, default=None, replace_entities=True):
        """
        Apply the given regex and return the first unicode string which
        matches. If there is no match, return the default value (``None`` if
        the argument is not provided).

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