json.JSONEncoder.iterencode drops entries from dict subclasses with false truthiness

[augusto-rehfeldt]

Bug report

Bug description:

Documented behaviour: json.dumps documentation: "Serialize obj to a JSON formatted str." JSONEncoder.iterencode documentation: "Encode the given object, o, and yield each string representation as available." Both describe serialization of the given object.

Expected: Both APIs return '{"a": 1}'.

Actual: json.dumps returns '{"a": 1}', while joined JSONEncoder.iterencode returns '{}'.

import json

class D(dict):
    def __bool__(self):
        return False

d = D(a=1)
if not all(type(k) is str and type(v) is int for k, v in d.items()):
    print("REFUTATION REJECTED: invalid input")
else:
    actual = json.dumps(d), ''.join(json.JSONEncoder().iterencode(d))
    reference = ''.join(json.JSONEncoder().iterencode(dict(d)))
    expected = reference, reference
    if actual != expected:
        print("REFUTATION CONFIRMED:", d, "actual:", actual, "expected:", expected)
    else:
        print("REFUTATION REJECTED: both APIs match the dictionary reference")

Output on Python 3.14.6 (Windows-11-10.0.26220-SP0), standard library json:

REFUTATION CONFIRMED: {'a': 1} actual: ('{"a": 1}', '{}') expected: ('{"a": 1}', '{"a": 1}')

This report was found and written by an automated property-testing tool I run (bugforge). The reproducer above was executed and its output is pasted unedited; no person reviewed the report before it was filed. The search script is in https://github.com/augusto-rehfeldt/bugforge-results/tree/main/json-20261003-130022-c2

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ZeroIntensity]

See #158748 (comment).