Introduction

Python 3.3 onwards includes in the standard library module 'lzma', providing support for working with LZMA and XZ compressed files via the XZ Utils C library (XZ Utils is in a sense LZMA v2). See:

• Python's lzma - http://docs.python.org/dev/library/lzma.html
• XZ Utils - http://tukaani.org/xz/

This code is a backport of the Python 3.3 standard library module 'lzma' for use on older versions of Python where it was not included. It is available from PyPI (released downloads only) and GitHub (repository):

• PyPI - http://pypi.python.org/pypi/backports.lzma/
• GitHub - https://github.com/peterjc/backports.lzma

There are some older Python libraries like PylibLZMA and PyLZMA but these are both using LZMA Utils (not XZ Utils, so they have no XZ support).

• PylibLZMA - http://pypi.python.org/pypi/pyliblzma
• PyLZMA - http://pypi.python.org/pypi/pylzma/
• LZMA Utils - http://tukaani.org/lzma/

Supported Platforms

The 'lmza' module provided with Python 3.3 should work on all the main operating systems, so in theory so too should this backport:

• Mac OS X: Tested under Python 2.6, 2.7, 3.0 to 3.4 inclusive
• Linux: Tested under Python 2.6, 2.7, 3.0 to 3.4 inclusive
• Windows: Untested (so far)

Other than some minor changes in the exceptions for some errors, based on the unit tests everything seems to be working fine.

Support under Python 2.6 and 2.7 appears to be working in that all the appropriate unit tests now pass. Supporting older verions of Python 2 is probably going to be too much work.

Installation

First you must install the XZ Utils C library, which on a Debian based Linux distribution can be done in one line:

$ sudo apt-get install liblzma-dev

Otherwise do this from source, this is what I do on Mac OS X:

$ curl -O http://tukaani.org/xz/xz-5.0.4.tar.gz
$ tar -zxvf xz-5.0.4.tar.gz
$ cd xz-5.0.4
$ ./configure --prefix=$HOME
$ make
$ make check
$ make install

Now you can install this 'lzma' backport. First download and decompress the source code, or clone the github repository:

$ git clone git://github.com/peterjc/backports.lzma.git
$ cd backports.lzma
$ python setup.py install
$ cd test
$ python test_lzma.py

To install for a specific version of Python, replace python (which will use the system's default Python) in the above with a specific version like python2, python2.6 or python3, python3.2, etc.

This should find the XZ Util header file and library automatically (and will check for a local install under your home directory). You should now be able to import the backport from Python 3 as shown below.

Usage

The expected usage is as follows if you want to prioritise the standard library provided lzma if present:

try:
    import lzma
except ImportError:
    from backports import lzma
#Then use lzma as normal, for example:
assert b"Hello!" == lzma.decompress(lzma.compress(b"Hello!"))

Please refer to the 'lzma' documentation online: http://docs.python.org/dev/library/lzma.html

Note that while 'lzma' should be available on Python 3.3, you can still install the backport. This is useful for two reasons, first testing the two act the same way, and second it is possible that your Python installation lacks the standard library 'lzma'. This can happen if Python was installed from source and XZ Utils was not available. If this was a systems level Python install, as a user you could still install XZ Utils and this backport under your own account.

This is using the shared 'backports' namespace introduced by Brandon Rhodes as documented here: http://pypi.python.org/pypi/backports/ and http://bitbucket.org/brandon/backports

Revisions

• v0.0.1 - January 2013
  • First public release
• v0.0.2 - April 2013
  • Fix the seekable attribute on Python 2 (Tomer Chachamu)
  • More search paths for lib/include headers (Wynn Wilkes)
• v0.0.3 - June 2014
  • Supports unicode filenames on Python 2 (Irving Reid)
• v0.0.4 - September 2014
  • Declare namespace package to avoid warnings (Ralph Bean)

Contributors

The initial Python lzma module implementation was by Per Øyvind Karlsen, which was then rewritten by Nadeem Vawda and included with Python 3.3. Based on this work, it was backported to also run on Python 2.6, 2.7 and 3.0, 3.1 and 3.2 by Peter Cock.

Later contributors include: Tomer Chachamu, Wynn Wilkes, Irving Reid, Ralph Bean

Bug Reports

Please report any reproducible bugs via the GitHub issue tracker at https://github.com/peterjc/backports.lzma/issues including details about your operating system, version of Python, XY Utils, the lzma backport etc. Reproducible test cases are particularly helpful.

If you can demonstrate a problem in this backport but not in the 'lzma' module included with Python 3.3 or later, then it is clearly something we will need to fix. Any issues in the 'lzma' module as bundled with Python 3.3 or later should be reported to the Python project at http://bugs.python.org instead.

Release Process

After testing locally and with TravisCI (see below), new releases are tagged in git as follows:

$ git tag backports.lzma.vX.X.X

I then use the following to upload a new release to the Python Packaging Index (PyPI):

$ python setup.py register sdist upload

The update then appears on http://pypi.python.org/pypi/backports.lzma/

Automated Testing

TravisCI is being used for continuous integration testing under 32-bit Linux, see https://travis-ci.org/peterjc/backports.lzma