import pprint

import pydantic

@dataclasses.dataclass(frozen=True)
class Z:
    inner: list
    __pydantic_config__ = {"ser_json_inf_nan": "constants"}

a = pydantic.TypeAdapter(Z)

pprint.pprint(a.core_schema)
# Output:
# {'cls': <class 'tests.parsing.test_utils.test_parse_then_unparse_nans.<locals>.Z'>,
#  'config': {'ser_json_inf_nan': 'constants', 'title': 'Z'},
#  'fields': ['inner'],
#  'metadata': {'pydantic.internal.needs_apply_discriminated_union': False},
#  'post_init': False,
#  'ref': 'tests.parsing.test_utils.test_parse_then_unparse_nans.<locals>.Z:1355051499120',
#  'schema': {'collect_init_only': False,
#             'computed_fields': [],
#             'dataclass_name': 'Z',
#             'fields': [{'init': True,
#                         'kw_only': False,
#                         'metadata': {'pydantic_js_annotation_functions': [<function get_json_schema_update_func.<locals>.json_schema_update_func at 0x0000013B4670E9E0>],
#                                      'pydantic_js_functions': []},
#                         'name': 'inner',
#                         'schema': {'items_schema': {'type': 'any'},
#                                    'strict': False,
#                                    'type': 'list'},
#                         'type': 'dataclass-field'}],
#             'type': 'dataclass-args'},
#  'slots': False,
#  'type': 'dataclass'}

pprint.pprint(a.dump_python(Z([math.nan]), mode="json"))
# Output:
# {'inner': [None]}