larzpack

Compact, MessagePack-compatible, deterministic serialization. Zero dependencies.

Encode Python data to compact binary — smaller than JSON, readable by any MessagePack tool — with one property plain MessagePack doesn't guarantee: the output is canonical. The same value always packs to the same bytes.

from larzpack import packb, unpackb

packb({"b": 2, "a": 1}) == packb({"a": 1, "b": 2})    # True — key order irrelevant
unpackb(packb([1, "two", 3.0, {"x": True}]))          # round-trips

Why the determinism matters

Integers use their smallest representation and map keys are emitted in sorted byte order, so identical logical values produce identical bytes. That makes the output safe to:

• hash / sign — a stable digest of a structure (pair with larzcrypt);
• content-address — use the bytes (or their hash) as a key;
• compare — two structures are equal iff their packed bytes are equal.

Plain json.dumps and most MessagePack encoders don't promise this — key order and integer widths can vary.

Why else

• Interoperable. It's the real MessagePack wire format for the core types, so other languages and tools can read it.
• Compact. Binary, with fix-forms for small ints/strings/arrays/maps.
• Zero dependencies. Pure standard library.

Install

pip install larzpack

Usage

from larzpack import packb, unpackb

blob = packb({"user": 42, "tags": ["a", "b"], "active": True, "score": 3.5})
unpackb(blob)     # {'user': 42, 'tags': ['a', 'b'], 'active': True, 'score': 3.5}

Supports None, bool, int, float, str, bytes, list, and dict.

Tests

python -m unittest discover -s tests -v   # 22 tests incl. spec bytes + determinism

The Larz stack

Pure-Python, zero-dependency building blocks: larz · larzchain · larzmoney · larzcrypt · larzdb · larzagent · larzchart · larzmark · larztask · larzvault · larzvm · larzcache · larzvalidate · larzid · larzrpc · larzstate · larzhttp · larzconf · larzcron · larzlimit · larzlog · larzcli · larzretry · larztime · larzpdf · larzpack

License

MIT © larz-scripter