Python yaml 模块，resolver() 实例源码

def __init__(self, **options):
        super(YamlReaderWriter, self).__init__(**options)

        try:
            import yaml
            import yaml.resolver
        except ImportError:
            raise RuntimeError('To use YAML, please install PyYAML first')

        #
        # The code to preserve order of items is taken from here:
        # https://stackoverflow.com/a/21048064/38611
        #

        _mapping_tag = yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG

        def dict_representer(dumper, data):
            return dumper.represent_dict(data.items())

        def dict_constructor(loader, node):
            return collections.OrderedDict(loader.construct_pairs(node))

        yaml.add_representer(collections.OrderedDict, dict_representer)
        yaml.add_constructor(_mapping_tag, dict_constructor)

        self.yaml = yaml

        self.default_dump_options = {
            'indent': 2,
            'default_flow_style': False,
        }

def _dict_representer(dumper, data):
    return dumper.represent_mapping(yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG, data.items())