How to use the graphistry.pygraphistry.util.error function in graphistry

def _check_bound_attribs(self, df, attribs, typ):
        cols = df.columns.values.tolist()
        for a in attribs:
            b = getattr(self, '_' + a)
            if b not in cols:
                util.error('%s attribute "%s" bound to "%s" does not exist.' % (typ, a, b))

def _check_mandatory_bindings(self, node_required):
        if self._source is None or self._destination is None:
            util.error('Both "source" and "destination" must be bound before plotting.')
        if node_required and self._node is None:
            util.error('Node identifier must be bound when using node dataframe.')

def _check_mandatory_bindings(self, node_required):
        if self._source is None or self._destination is None:
            util.error('Both "source" and "destination" must be bound before plotting.')
        if node_required and self._node is None:
            util.error('Node identifier must be bound when using node dataframe.')

g.nodes(vs2).bind(point_color='community').plot()
        """

        def get_edgelist(ig):
            idmap = dict(enumerate(ig.vs[self._node]))
            for e in ig.es:
                t = e.tuple
                yield dict({self._source: idmap[t[0]], self._destination: idmap[t[1]]},
                            **e.attributes())

        self._check_mandatory_bindings(False)
        if self._node is None:
            ig.vs[Plotter._defaultNodeId] = [v.index for v in ig.vs]
            self._node = Plotter._defaultNodeId
        elif self._node not in ig.vs.attributes():
            util.error('Vertex attribute "%s" bound to "node" does not exist.' % self._node)

        edata = get_edgelist(ig)
        ndata = [v.attributes() for v in ig.vs]
        nodes = pandas.DataFrame(ndata, columns=ig.vs.attributes())
        cols = [self._source, self._destination] + ig.es.attributes()
        edges = pandas.DataFrame(edata, columns=cols)
        return (edges, nodes)