Subclassing PrettyPrinter.format doesn't work in all cases

Bug report

Bug description:

See also the earlier fixed https://github.com/python/cpython/issues/73036. This appears to have only been a partial fix, or it has regressed.

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)

This outputs:

{'item': SENTINAL,
 'dict': {'a': SENTINAL},
 'dict_key': {HASHABLE_SENTINAL: 1},
 'OrderedDict': OrderedDict({'a': <object object at 0x1041f4660>}),
 'OrderedDict_key': OrderedDict([(HASHABLE_SENTINAL, 1)]),
 'list': [SENTINAL],
 'tuple': (SENTINAL,),
 'set': {<object object at 0x1041f4660>},
 'frozenset': frozenset({<object object at 0x1041f4660>}),
 'mappingproxy': mappingproxy({'a': <object object at 0x1041f4660>}),
 'mappingproxy_key': mappingproxy({HASHABLE_SENTINAL: 1}),
 'SimpleNamespace': namespace(a=<object object at 0x1041f4660>),
 'defaultdict': defaultdict(<class 'list'>,
                            {'a': SENTINAL}),
 'defaultdict_key': defaultdict(<class 'list'>,
                                {HASHABLE_SENTINAL: 1}),
 'Counter': Counter({'a': <object object at 0x1041f4660>}),
 'Counter_key': Counter({<__main__._hashable object at 0x1045e4d70>: 1}),
 'deque': deque([<object object at 0x1041f4660>])}

Every instance of < in that output is a bug.

CPython versions tested on:

3.13

Operating systems tested on:

macOS

Linked PRs

• gh-133238

まず reproducer を実行し、pprint.PrettyPrinter.format を調べます。特に、列挙されたコンテナ型とその内容をどのように処理するかを確認します。各出力を期待されるカスタムフォーマットと比較し、その後、override がバイパスされるケースの回帰テストを追加します。完了の条件は、reproducer に示されるすべての または repr がサブクラスの format メソッドに従うことです。