PyHeatshrink

Compression using the Heatshrink algorithm in Python 3.

Installation

From PyPI:

$ pip install heatshrink2

Usage

Files/Streams

The file interface attempts to imitate the behaviour of the built-in file object and other file-like objects (E.g. bz2.BZ2File), thus you can expect all methods implemented in file to also be available.

You can open a heatshrink file by using the open function:

>>> import heatshrink2
>>> with heatshrink2.open('data.bin', 'wb') as fout:
...     fout.write(b"Is there anybody in there?")
...
26
>>>

You can also use HeatshrinkFile directly:

>>> from heatshrink2 import HeatshrinkFile
>>> with HeatshrinkFile('data.bin') as fin:
...     print(fin.read(256))
...
b'Is there anybody in there?'
>>> with HeatshrinkFile('data.bin') as fin:
...     for line in fin:
...         print(line)
...
b'Is there anybody in there?'
>>>

Byte strings

The encoder accepts any iterable and returns a byte string containing encoded (compressed) data.

>>> import heatshrink2
>>> heatshrink2.compress(b'a string')
b'\xb0\xc8.wK\x95\xa6\xddg'
>>>

The decoder accepts any object that implements the buffer protocol and returns a byte representation of the decoded data.

>>> import heatshrink2
>>> heatshrink2.decompress(b'\xb0\xc8.wK\x95\xa6\xddg')
b'a string'
>>>

Parameters

Both the encoder and decoder allow providing window_sz2 and lookahead_sz2 keywords:

window_sz2 - The window size determines how far back in the input can be searched for repeated patterns. A window_sz2 of 8 will only use 256 bytes (2^8), while a window_sz2 of 10 will use 1024 bytes (2^10). The latter uses more memory, but may also compress more effectively by detecting more repetition.

lookahead_sz2 - The lookahead size determines the max length for repeated patterns that are found. If the lookahead_sz2 is 4, a 50-byte run of 'a' characters will be represented as several repeated 16-byte patterns (2^4 is 16), whereas a larger lookahead_sz2 may be able to represent it all at once. The number of bits used for the lookahead size is fixed, so an overly large lookahead size can reduce compression by adding unused size bits to small patterns.

input_buffer_size - How large an input buffer to use for the decoder. This impacts how much work the decoder can do in a single step, and a larger buffer will use more memory. An extremely small buffer (say, 1 byte) will add overhead due to lots of suspend/resume function calls, but should not change how well data compresses.

Check out the heatshrink configuration page for more details.

For more use cases, please refer to the tests folder.

Command line

The command line tool can compress and decompress files.

Below is an example of the compress and decompress subcommands.

$ ls -l tests/files/foo.txt
-rw-rw-r-- 1 erik erik 3970 jan  5 12:23 tests/files/foo.txt
$ python -m heatshrink2 compress tests/files/foo.txt foo.hs
$ ls -l foo.hs
-rw-rw-r-- 1 erik erik 2727 jan  5 12:24 foo.hs
$ python -m heatshrink2 decompress foo.hs foo.txt
$ cmp tests/files/foo.txt foo.txt

Benchmarks

The benchmarks check compression/decompression against a ~6MB file:

$ python scripts/benchmark.py

Testing

Running tests is as simple as doing:

$ python setup.py build_ext -b .
$ python -m unittest

License

ISC license