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README.md

Edge Python JSON

JSON serialization, deserialization, and round-tripping shipped as a .wasm plugin. Scripts see json as ordinary.

from json import dumps, loads

data = loads('{"name":"ada","tags":["math","cs"],"score":91.5}')
print(data["name"], data["tags"][0])
print(dumps({"k": [1, 2, 3], "ok": True}))

API

Conventions

  • Types map straight through. null<->None, true/false<->bool, JSON numbers split into int (i128) and float (f64), strings are UTF-8, arrays are list, objects are dict. Python tuple/set serialize as JSON arrays but parse back as list.
  • Errors raise typed exceptions. Parser failures surface as ValueError with the byte offset; non-serializable values raise TypeError naming the offending type unless default= is supplied.
  • Compact output by default. No whitespace, dict insertion order preserved. Integer-valued floats keep a trailing .0 so a round-trip returns the same Python type.
  • CPython parity. Both functions accept the full kwargs of json.dumps / json.loads; defaults match CPython.

loads

loads(s, *, cls=None, object_hook=None, parse_float=None,
      parse_int=None, parse_constant=None, object_pairs_hook=None)
loads("9223372036854775808") # -> 2**63 (int via i128 wire tag)
loads("1.5e3") # -> 1500.0
loads('{"k":"v"}') # -> {"k": "v"}
loads("NaN") # -> float('nan')   (also Infinity / -Infinity)

Each kwarg fires at the matching production and replaces the default decoding for that node.

Kwarg Type Behaviour
object_hook callable(dict) -> any Called with every completed object; the return value replaces the dict.
object_pairs_hook callable(list[[key, val]]) -> any Wins over object_hook when both are set. Receives a list of [key, value] lists.
parse_float callable(str) -> any Receives the raw float source token; return value used as-is.
parse_int callable(str) -> any Receives the raw int source token; return value used as-is.
parse_constant callable(str) -> any Fires for "NaN", "Infinity", "-Infinity".
cls callable Reserved for an alternate decoder class (currently behaves like default decoding).

dumps

dumps(obj, *, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, default=None, sort_keys=False)
dumps(1.0) # -> '1.0'
dumps((1, 2, 3)) # -> '[1,2,3]'
dumps({"a": 1, "b": None}) # -> '{"a":1,"b":null}'
dumps({"b": 2, "a": 1}, sort_keys=True) # -> '{"a":1,"b":2}'
dumps("héllo", ensure_ascii=False) # -> '"héllo"'
Kwarg Default Behaviour
indent None Integer pretty-print width. With indent, key separator becomes ": " by default.
sort_keys False Sort dict keys ASCII-lexicographically before emit.
ensure_ascii True Escape characters >= U+0080 as \uXXXX. When False, emit the UTF-8 bytes directly.
check_circular True Bound recursive nesting at 200 levels; deeper raises ValueError("Circular reference detected").
allow_nan True Emit NaN / Infinity / -Infinity for non-finite floats. With False, they raise ValueError.
skipkeys False Silently skip non-str dict keys instead of raising TypeError.
separators (",", ":") compact, (",", ": ") with indent Two-element tuple (item_sep, key_sep).
default None Callable that receives any non-serializable value; its return is re-serialized.
cls None Encoder class with an .encode(obj) method; if supplied, the whole walk is delegated to it.

Round-tripping

dumps(loads(s)) is idempotent for canonical shapes: output parsed then re-dumps'd returns the same text.

How it works

Compiles to wasm32-unknown-unknown (cdylib) against the wasm-pdk v0.1.0 ABI. loads builds Python values through the handle ABI (new_dict/new_list, set_item, primitives via encode); dumps walks the input handle with type_of/iter/len/get_item. Hooks are forwarded to the caller's Python callable via Handle::call("__call__", args).

Single-pass tokenizer + recursive-descent parser, ~95 KB stripped. Plugin memory recycles per call through a static 4 MB pool, so long-running workers stay flat. The upstream wasm-pdk ABI leaks ~8 bytes per host call, so a single worker session caps at roughly 500 k plugin calls; recycle the worker periodically for unbounded streaming.

Pre-built .wasm is served from https://cdn.edgepython.com/std/json.wasm, deployed by the Std workflow.

License

MIT OR Apache-2.0