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PPMd compression/decompression library

Project description

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Introduction

pyppmd module provides classes and functions for compressing and decompressing text data, using PPM(Prediction by partial matching) compression algorithm which has several variations of implementations. PPMd is the implementation by Dmitry Shkarin. PyPPMD use Igor Pavlov’s range coder introduced in 7-zip.

The API is similar to Python’s bz2/lzma/zlib module.

Some parts of th codes are derived from 7-zip, pyzstd and ppmd-cffi.

Development status

A project status is considered as Stable.

Extra input byte

PPMd algorithm and implementation is designed to use Extra input byte. The encoder will omit a last null (b”0”) byte when last byte is b”0”. You may need to provide an extra null byte when you don’t get expected size of extracted data.

You can do like as:

dec = pyppmd.Ppmd7Decoder(max_order=6, mem_size=16 << 10)
result = dec.decode(compressed, length)
if len(result) < length:
    if dec.needs_input:
        # ppmd need an extra null byte
        result += dec.decode(b"\0", length - len(result))
    else:
        result += dec.decode(b"", length - len(result))

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