zctw 0.1.1

Python implementation of Context Tree Weighting (CTW) lossless compression

zctw

Python implementation of Context Tree Weighting (CTW) lossless compression.

Install

pip install zctw

Usage

from zctw import CTWCompressor, CTWSettings

# Use default settings
compressor = CTWCompressor()

# Or customize settings
settings = CTWSettings(treedepth=8, maxnrnodes=4194304)
compressor = CTWCompressor(settings)

# Compress data
original = b"Hello, World! This is a test of the CTW compression algorithm."
compressed = compressor.encode(original)

# Decompress
decompressed = compressor.decode(compressed)

print(f"Original: {len(original)} bytes")
print(f"Compressed: {len(compressed)} bytes")
print(f"Decompressed matches: {original == decompressed}")

CLI

# Encode a file
zctw e input.txt output.zctw

# Decode a file
zctw d output.zctw input_decoded.txt

# Show file info
zctw i output.zctw

CLI Options

• -dX: Set maximum tree depth (1-12)
• -tX: Set maximum number of tries in tree array (1-32)
• -nX: Set maximum number of nodes (supports K/M suffix, e.g., 4M)
• -fX: Set maximum file buffer size (supports K/M suffix)
• -bX: Set maximum value of log beta
• -s: Disable strict tree pruning
• -r: Enable weighting at root nodes
• -k: Use Krichevski-Trofimov estimator instead of Zero-Redundancy
• -y: Force overwriting of existing files
• -lX: Enable logging to file X

API

CTWSettings

@dataclass
class CTWSettings:
    treedepth: int          # max depth of trees, excluding root (default: 6)
    maxnrnodes: int         # max nodes in tree array (default: 4194304)
    maxnrtries: int        # max tries in hash table (default: 32)
    filebufsize: int       # actual file buffer size (default: 4194304)
    maxfilebufsize: int    # max file buffer size (default: 4194304)
    strictpruning: bool    # use strict pruning method (default: True)
    maxlogbeta: int        # max value of logbeta (default: 1024)
    rootweighting: bool    # perform weighting at root node (default: False)
    use_zeroredundancy: bool # use zero-redundancy estimator (default: True)

CTWCompressor

class CTWCompressor:
    def __init__(self, settings: CTWSettings | None = None)
    def encode(self, data: bytes) -> bytes
    def decode(self, compressed: bytes) -> bytes

Development

git clone https://github.com/daedalus/zctw.git
cd zctw
pip install -e ".[test]"

# run tests
pytest

# format
ruff format src/ tests/

# lint
ruff check src/ tests/

# type check
mypy src/

License

MIT License - see LICENSE file.