def _stub_tag(constructor, node):
    """Stub a constructor with a dictionary."""
    seen = getattr(constructor, '_stub_seen', None)
    if seen is None:
        seen = constructor._stub_seen = set()
    if node.tag not in seen:
        print('YAML tag {} is not supported'.format(node.tag))
        seen.add(node.tag)
    return {}
