Lib/json/__init__.py (part 3)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/json/__init__.py ↗

This annotation covers the top-level json API. See modules_json4_detail for JSONDecoder, scanstring, and the C-level decode fast path.

Map

Lines	Symbol	Role
1-80	json.dumps	Serialize object to JSON string
81-160	json.loads	Deserialize JSON string to object
161-240	json.dump / json.load	File-based serialize/deserialize
241-340	JSONEncoder.default	Override for custom type serialization
341-500	JSONEncoder.encode	Full encoding with ensure_ascii, sort_keys

Reading

json.dumps

# CPython: Lib/json/__init__.py:230 dumps
def dumps(obj, *, skipkeys=False, ensure_ascii=True, check_circular=True,
          allow_nan=True, cls=None, indent=None, separators=None,
          default=None, sort_keys=False, **kw):
    if cls is None:
        cls = JSONEncoder
    return cls(
        skipkeys=skipkeys, ensure_ascii=ensure_ascii,
        check_circular=check_circular, allow_nan=allow_nan, indent=indent,
        separators=separators, default=default, sort_keys=sort_keys,
        **kw).encode(obj)

json.dumps creates a JSONEncoder and calls encode. ensure_ascii=True escapes non-ASCII characters as \uXXXX. indent enables pretty-printing. separators=(',', ':') produces compact JSON. sort_keys sorts dict keys for deterministic output.

JSONEncoder.default

# CPython: Lib/json/encoder.py:170 JSONEncoder.default
def default(self, o):
    raise TypeError(f'Object of type {type(o).__name__} '
                    f'is not JSON serializable')

default is called for non-serializable objects. Subclass and override to add support for datetime, Decimal, UUID, etc.:

class DateEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime.datetime):
            return obj.isoformat()
        return super().default(obj)

JSONEncoder.encode

# CPython: Lib/json/encoder.py:196 JSONEncoder.encode
def encode(self, o):
    if isinstance(o, str):
        if self.ensure_ascii:
            return encode_basestring_ascii(o)
        else:
            return encode_basestring(o)
    chunks = self.iterencode(o, _one_shot=True)
    if not isinstance(chunks, (list, tuple)):
        chunks = list(chunks)
    return ''.join(chunks)

iterencode generates the JSON string lazily. For simple string inputs, the fast path uses encode_basestring_ascii (C implementation). The _one_shot=True flag enables an optimized single-pass encoder in the C extension.

gopy notes

json.dumps is module/json.Dumps in module/json/module.go. JSONEncoder.encode uses a recursive Go function. ensure_ascii is applied per-character using unicode.IsPrint. JSONEncoder.default calls objects.CallMethod on the encoder.