The error code doesn’t make sense to me because the return value from

_matchnodes

should always have

len

because it’s a list

def _matchnodes(self, matching, names):
        if not matching or not names:
            return matching
        name = names[0]
        assert name
        nextnames = names[1:]
        resultnodes = []
        for node in matching:
            if isinstance(node, nodes.Item):
                if not names:
                    resultnodes.append(node)
                continue
            assert isinstance(node, nodes.Collector)
            if node.nodeid in self._node_cache:
                rep = self._node_cache[node.nodeid]
            else:
                rep = collect_one_node(node)
                self._node_cache[node.nodeid] = rep
            if rep.passed:
                has_matched = False
                for x in rep.result:
                    # TODO: remove parametrized workaround once collection structure contains parametrization
                    if x.name == name or x.name.split("[")[0] == name:
                        resultnodes.extend(self.matchnodes([x], nextnames))
                        has_matched = True
                # XXX accept IDs that don't have "()" for class instances
                if not has_matched and len(rep.result) == 1 and x.name == "()":
                    nextnames.insert(0, name)
                    resultnodes.extend(self.matchnodes([x], nextnames))
            else:
                # report collection failures here to avoid failing to run some test
                # specified in the command line because the module could not be
                # imported (#134)
                node.ihook.pytest_collectreport(report=rep)
        return resultnodes