crous

A compact, canonical binary serializer and human-readable alternative to JSON — pure Python.

Overview

Crous is a production-grade binary serialization format that provides:

• Compact binary encoding — 2×–5× smaller than equivalent JSON
• Human-readable text notation — unique syntax with deterministic binary mapping
• Zero-copy decoding — borrow directly from input buffers
• Block-framed format — per-block XXH64 checksums for data integrity
• File I/O — load() / dump() familiar API, like json.load / json.dump
• Cross-language — wire-compatible with the Rust implementation

Installation

pip install crous

Quick Start

import crous

# Encode any Python object
data = crous.encode({"name": "Alice", "age": 30, "active": True})
print(data[:7])  # b'CROUSv1'

# Decode back to Python
obj = crous.decode(data)
print(obj)  # {'name': 'Alice', 'age': 30, 'active': True}

File I/O

import crous

# Write to a .crous file (like json.dump)
crous.dump({"name": "Alice", "age": 30}, "data.crous")

# Read from a .crous file (like json.load)
obj = crous.load("data.crous")
print(obj)  # {'name': 'Alice', 'age': 30}

# Append a value to an existing file
crous.append({"event": "stop"}, "log.crous")

# Lossless round-trip with Value objects
from crous.value import Value
crous.dump_values([Value.str_("hello"), Value.uint(42)], "typed.crous")
values = crous.load_values("typed.crous")
print(values[0].type)  # ValueType.STR

Human-Readable Text Format

{
    name: "Alice";
    age: 30;
    tags: ["admin", "user"];
    config: {
        theme: "dark";
        notifications: true;
    };
    avatar: b64#iVBORw0KGgo=;
}

Parse and pretty-print:

import crous

text = '{ name: "Alice"; age: 30; }'
value = crous.parse_text(text)
print(crous.pretty_print(value))

Encoder / Decoder Classes

from crous.encoder import Encoder
from crous.value import Value

enc = Encoder()
enc.enable_dedup()          # Enable string deduplication
enc.encode_value(Value.from_python({"key": "value"}))
data = enc.finish()

from crous.decoder import Decoder

dec = Decoder(data)
values = dec.decode_all()
print(values[0].to_python())

Wire Format

File:    [Header 8B] [Block]* [Trailer Block]
Header:  "CROUSv1" (7B) | flags (1B)
Block:   type(1B) | length(varint) | compression(1B) | checksum(8B) | payload

The format is deterministic: the same input always produces the same bytes.

Cross-Language Compatibility

Data encoded by the pure-Python crous package is fully wire-compatible with the Rust implementation (crous-core). Files can be written in Python and read in Rust, or vice versa.

License

Licensed under either of:

• MIT License (LICENSE-MIT)
• Apache License, Version 2.0 (LICENSE-APACHE)

at your option.