import collections
import pprint
import types


SENTINAL = object()


class _hashable:
    def __hash__(self):
        return 1


HASHABLE_SENTINAL = _hashable()


class CustomPrettyPrinter(pprint.PrettyPrinter):
    def format(self, obj, context, maxlevels, level):
        if obj is SENTINAL:
            return "SENTINAL", True, False
        elif obj is HASHABLE_SENTINAL:
            return "HASHABLE_SENTINAL", True, False
        else:
            return super().format(obj, context, maxlevels, level)


if __name__ == "__main__":
    printer = CustomPrettyPrinter(sort_dicts=False)

    test_data = {
        "item": SENTINAL,
        "dict": {"a": SENTINAL},
        "dict_key": {HASHABLE_SENTINAL: 1},
        "OrderedDict": collections.OrderedDict({"a": SENTINAL}),
        "OrderedDict_key": collections.OrderedDict({HASHABLE_SENTINAL: 1}),
        "list": [SENTINAL],
        "tuple": (SENTINAL,),
        "set": {SENTINAL},
        "frozenset": frozenset({SENTINAL}),
        "mappingproxy": types.MappingProxyType({"a": SENTINAL}),
        "mappingproxy_key": types.MappingProxyType({HASHABLE_SENTINAL: 1}),
        "SimpleNamespace": types.SimpleNamespace(a=SENTINAL),
        "defaultdict": collections.defaultdict(list, {"a": SENTINAL}),
        "defaultdict_key": collections.defaultdict(list, {HASHABLE_SENTINAL: 1}),
        "Counter": collections.Counter({"a": SENTINAL}),
        "Counter_key": collections.Counter({HASHABLE_SENTINAL: 1}),
        "deque": collections.deque([SENTINAL]),
    }

    printer.pprint(test_data)