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Distlib evolved out of packaging¶
Distlib is a library which implements low-level functions that relate to packaging and distribution of Python software. It consists in part of the functions in the packaging Python package, which was intended to be released as part of Python 3.3, but was removed shortly before Python 3.3 entered beta testing.
What was the problem with packaging?¶
The packaging software just wasn’t ready for inclusion in the Python standard library. The amount of work needed to get it into the desired state was too great, given the number of people able to work on the project, the time they could devote to it, and the Python 3.3 release schedule.
The approach taken by packaging was seen to be a good one: to ensure interoperability and consistency between different tools in the packaging space by defining standards for data formats through PEPs, and to do away with the ad hoc nature of installation encouraged by the distutils approach of using executable Python code in setup.py. Where custom code was needed, it could be provided in a standardised way using installation hooks.
While some very good work was done in defining PEPs to codify some of the best practices, packaging suffered from some drawbacks, too:
Not all the PEPs may have been functionally complete, because some important use cases were not considered – for example, built (binary) distributions for Windows.
It continued the command-based design of distutils, which had resulted in distutils being difficult to extend in a consistent, easily understood, and maintainable fashion.
Some important features required by distribution authors were not considered – for example:
- Access to data files stored in Python packages.
- Support for plug-in extension points.
- Support for native script execution on Windows.
These features are supported by third-party tools (like setuptools / Distribute) using pkg_resources, entry points and console scripts.
There were a lot of rough edges in the packaging implementation, both in terms of bugs and in terms of incompletely implemented features. This can be seen (with the benefit of hindsight) as due to the goals being set too ambitiously; the project developers bit off more than they could chew.
How Distlib can help¶
The idea behind Distlib is expressed in this python-dev mailing-list post, though a different name was suggested for the library. Basically, Distlib contains the implementations of the packaging PEPs and other low-level features which relate to packaging, distribution, and deployment of Python software. If Distlib can be made genuinely useful, then it is possible for third-party packaging tools to transition to using it. Their developers and users then benefit from standardised implementation of low-level functions, time saved by not having to reinvent wheels, and improved interoperability between tools.
How you can help¶
If you have some time and the inclination to improve the state of Python packaging, then you can help by trying out Distlib, raising issues where you find problems, contributing feedback and/or patches to the implementation, documentation, and underlying PEPs.
Distlib currently offers the following features:
- The package distlib.database, which implements a database of installed distributions, as defined by PEP 376, and distribution dependency graph logic. Support is also provided for non-installed distributions (i.e. distributions registered with metadata on an index like PyPI), including the ability to scan for dependencies and building dependency graphs.
- The package distlib.index, which implements an interface to perform operations on an index, such as registering a project, uploading a distribution or uploading documentation. Support is included for verifying SSL connections (with domain matching) and signing/verifying packages using GnuPG.
- The package distlib.metadata, which implements distribution metadata as defined by PEP 426, PEP 345, PEP 314 and PEP 241.
- The package distlib.markers, which implements environment markers as defined by PEP 426.
- The package distlib.manifest, which implements lists of files used in packaging source distributions.
- The package distlib.locators, which allows finding distributions, whether on PyPI (XML-RPC or via the “simple” interface), local directories or some other source.
- The package distlib.resources, which allows access to data files stored in Python packages, both in the file system and in .zip files.
- The package distlib.scripts, which allows installing of scripts with adjustment of shebang lines and support for native Windows executable launchers.
- The package distlib.version, which implements version specifiers as defined by PEP 440 / PEP 426, but also support for working with “legacy” versions (setuptools/distribute) and semantic versions.
- The package distlib.wheel, which provides support for building and installing from the Wheel format for binary distributions (see PEP 427).
- The package distlib.util, which contains miscellaneous functions and classes which are useful in packaging, but which do not fit neatly into one of the other packages in distlib.* The package implements enhanced globbing functionality such as the ability to use ** in patterns to specify recursing into subdirectories.
Python version and platform compatibility¶
Distlib is intended to be used on any Python version >= 2.6 and is tested on Python versions 2.6, 2.7, 3.1, 3.2, and 3.3 on Linux, Windows, and Mac OS X (not all versions are tested on all platforms, but are expected to work correctly).
The project has reached alpha status in its development: there is a test suite and it has been exercised on Windows, Ubuntu and Mac OS X. To work with the project, you can download a release from PyPI, or clone the source repository or download a tarball from it.
Coverage results are available at:
Continuous integration test results are available at:
The source repository for the project is on BitBucket:
You can leave feedback by raising a new issue on the issue tracker (BitBucket registration not necessary, but recommended).