Many pure python tools that have a special cases for dict should accept frozendict as well.

I'll fix the ones in collections. Some other priorities are pprint and ElementTree

Here's a rg dict | rg isinstance scan of the Lib directory:

unittest/mock.py:        if isinstance(self.in_dict, str):
trace.py:                             if isinstance(d, dict)]
rlcompleter.py:        if namespace and not isinstance(namespace, dict):
rlcompleter.py:                        isinstance(thisobject.__dict__.get(word),
tomllib/_parser.py:            if not isinstance(cont, dict):
tomllib/_parser.py:    if isinstance(value, (dict, list)):
tomllib/_parser.py:        if isinstance(value, (dict, list)):
tomllib/_parser.py:        if isinstance(float_value, (dict, list)):
multiprocessing/managers.py:                if not isinstance(method_to_typeid, dict):
functools.py:           (kwds is not None and not isinstance(kwds, dict)) or
functools.py:           (namespace is not None and not isinstance(namespace, dict))):
pprint.py:        if isinstance(object, self._dict_items_view):
turtle.py:        if isinstance(pen, dict):
optparse.py:                not isinstance(self.callback_kwargs, dict)):
optparse.py:        elif isinstance(other, dict):
linecache.py:    if module_globals is not None and not isinstance(module_globals, dict):
xml/etree/ElementTree.py:        if not isinstance(attrib, dict):
_pyrepl/input.py:        if isinstance(d, dict):
tkinter/__init__.py:    if isinstance(cnfs, dict):
tkinter/__init__.py:        if isinstance(cnf, (dict, tuple)):
_pyrepl/base_eventqueue.py:            if isinstance(k, dict):
test/_test_multiprocessing.py:    def test_dict_isinstance(self):
_pyrepl/readline.py:    if not isinstance(namespace, dict):
logging/config.py:        if not isinstance(value, ConvertingDict) and isinstance(value, dict):
logging/config.py:                    elif isinstance(qspec, dict):
logging/config.py:                        elif isinstance(lspec, dict):
logging/config.py:                            assert isinstance(d, dict)
test/test_pyrepl/test_terminfo.py:                        isinstance(ncurses_data[key], dict)
test/test_pyrepl/test_terminfo.py:                            isinstance(ncurses_data[key], dict)
test/test_launcher.py:        if isinstance(value, dict):
test/test_launcher.py:            tags = [t for t in company_data if isinstance(company_data[t], dict)]
test/test_launcher.py:            tags = [t for t in company_data if isinstance(company_data[t], dict)]
test/test_isinstance.py:        self.assertFalse(issubclass(dict, float|str))
test/test_marshal.py:    elif isinstance(obj, dict):
test/test_format.py:    if isinstance(args, dict):
test/test_build_details.py:                        self.assertFalse(isinstance(sys.implementation.version, dict))
_pydecimal.py:        elif not isinstance(traps, dict):
_pydecimal.py:        elif not isinstance(flags, dict):
_pydecimal.py:        if not isinstance(d, dict):
collections/__init__.py:        if not isinstance(other, dict):
collections/__init__.py:        if not isinstance(other, dict):
collections/__init__.py:        if isinstance(other, dict):
collections/__init__.py:        if isinstance(other, dict):
test/test_module/__init__.py:        self.assertTrue(isinstance(foo.__dict__, dict))
profiling/sampling/heatmap_collector.py:            if isinstance(data, dict):
test/test_code.py:                if isinstance(globalvars, dict):
test/test_urllib2_localnet.py:        assert isinstance(users, dict)
annotationlib.py:            or isinstance(self.__cell__, dict)
annotationlib.py:        if isinstance(self.__cell__, dict):
annotationlib.py:                if isinstance(self.__cell__, dict) and isinstance(other.__cell__, dict)
annotationlib.py:                if isinstance(self.__cell__, dict) else id(self.__cell__),
annotationlib.py:        if not isinstance(ann, dict):
annotationlib.py:    if not isinstance(ann, dict):
test/test_io/test_general.py:                if isinstance(v, dict):
test/test_compiler_assemble.py:            elif isinstance(value, dict):
json/encoder.py:                    elif isinstance(value, dict):
json/encoder.py:                    elif isinstance(value, dict):
json/encoder.py:        elif isinstance(o, dict):
plistlib.py:            if not isinstance(self.stack[-1], dict):
plistlib.py:        if self.current_key or not isinstance(self.stack[-1], dict):
plistlib.py:        elif isinstance(value, dict):
plistlib.py:        if isinstance(value, dict):
plistlib.py:        elif isinstance(value, dict):
test/test_tomllib/burntsushi.py:    elif isinstance(obj, dict):
test/test_tomllib/burntsushi.py:    if isinstance(obj, dict):
inspect.py:        if isinstance(dict_obj, (staticmethod, types.BuiltinMethodType)):
inspect.py:        elif isinstance(dict_obj, (classmethod, types.ClassMethodDescriptorType)):
inspect.py:        elif isinstance(dict_obj, property):
inspect.py:            if isinstance(slots, dict) and name in slots:
inspect.py:            (kwdefaults is None or isinstance(kwdefaults, dict)))
xmlrpc/client.py:        if isinstance(item, dict):
test/test_importlib/resources/zip.py:        if isinstance(contents, dict):
importlib/_bootstrap_external.py:    if not isinstance(module_globals, dict):
test/test_descrtut.py:    >>> isinstance([], dict)
enum.py:    if isinstance(obj, dict):
test/test_import/test_lazy_imports.py:            assert isinstance(sys.lazy_modules, dict), "sys.lazy_modules is not a dict"
test/test_type_annotations.py:                if not isinstance(self.my_annotations, dict):
test/test_type_annotations.py:                if not isinstance(value, dict):
dataclasses.py:    elif isinstance(obj, dict):
test/string_tests.py:        elif isinstance(obj, dict):
test/test_pyclbr.py:                if (not isinstance(classdict[name], ClassMethodType) or
compression/zstd/_zstdfile.py:        if options is not None and not isinstance(options, dict):
compression/zstd/__init__.py:    if not isinstance(dict_size, int):
compression/zstd/__init__.py:    if not isinstance(zstd_dict, ZstdDict):
compression/zstd/__init__.py:    if not isinstance(dict_size, int):

Linked PRs

• gh-145060
• gh-145125
• gh-145508
• gh-146295
• gh-146465
• gh-146466

Start by reviewing collections/init.py and the mentioned pprint.py and xml/etree/ElementTree.py locations, then read the linked PRs to determine which cases remain open. Compare the existing dict checks and related tests in each affected module; done means the agreed remaining pure-Python tools consistently handle frozendict without regressing dict behavior.