a small Distutils2 foretaste

Notice: If you didn't follow what's going on in the packaging world, you can read this.

The first public version of Distutils2 will be 1.0a1, and is scheduled for April 30th.

We are working on implementing the various PEPs, removing the bad bits inherited from Distutils, keeping the good ones, and adding the work that was done in Distribute, like the Python 3 work (and grabbing the good bits of Setuptools as well, like the test command.) I have also proposed a GSOC project, and I hope it will be picked by the PSF, to boost the work.

In any case, lots of tasks will not be ready for 1.0a1, and will be shipped later. But I think its important to release what we currently have since it's also a result of over 1 year of work I have been doing within the stdlib. As a reminder: I reverted this work in Python, making Distutils there pretty similar to 2.6's, and I've forked this work to create distutils2.

Anyways, this blog entry is focusing on describing some of the features you will find in Distutils2 today.

The code is located in the new Python Mercurial repository (http://hg.python.org/distutils2).

Distutils2 philosophy

One of the key point of Distutils2 is to try to provide tools for third-party projects like Pip, PyPM, etc. without forcing them to adopt the everything-is-a-distutils-command philosophy. People have suffered from this in the past, and this problem was probably one of the reason the Setuptools project has to patch Distutils' code all over the place.

I am therefore trying to think about Distutils2 as two distinct things:

  1. a python packaging framework with tools anyone can use
  2. a python package manager based on CLI commands people can use to build, upload, install packages.

The way 2. is working today in Distutils has been very controversial, and they are other tools out there based on other philosophies. I'll focus on making 1. as useful as possible for all tools, without forcing them to adopt 2. But also to enhance/fix 2.

There are key features to add in Distutils2 to make the CLI command system more useful. For instance, adding a configure command that will take all compiling options and generate a configuration file that can be consumed by other commands (build or install for instance) will probably make people life easier. This has been done by 4Suite, and this will be done in Distutils2.

In the Framework part, we already have two interesting modules you can already use:

The version module

The version module is the implementation of PEP 376. It provides among other things:
- The NormalizedVersion class you can use to work with PEP 376 version - The suggest_normalized_version() function you can use to try to transform any version into a PEP 376-compatible version. This function is based on what we have learned by looking at the projects released at PyPI.

So, if you need to compare versions, you can create instances of NormalizedVersion using the string representation of the version, and use any comparison operator.

from distutils2.version import NormalizedVersion

>>> NormalizedVersion('1.2a1') < NormalizedVersion('1.2')

True

In case the version is not PEP 376 compatible, the class will throw an exception

NormalizedVersion('1.2-a1')

Traceback (most recent call last):

...

distutils2.errors.IrrationalVersionError: 1.2-a1

And for these "irrational versions" ;), you can use suggest_normalized_version to try to convert them:

from distutils2.version import suggest_normalized_version

>>> suggest_normalized_version('1.2-a1')

'1.2a1'

>>> NormalizedVersion(suggest_normalized_version('1.2-a1'))

NormalizedVersion('1.2a1')

The metadata module

The metadata module implements PEP 345 (the new metadata) but also works with old metadata versions. It provides a DistributionMetadata class you can use to read or write metadata files (those PKG-INFO file you can find in any release). This class is compatible with all versions of Metadata:
- 1.0 : PEP 241 - 1.1 : PEP 314 - 1.2 : PEP 345

The PEP 345 implementation supports the micro-language for the environment markers, and displays warnings when versions that are supposed to be PEP 386 are violating the scheme.

Reading metadata

The DistributionMetadata class can be instanciated with the path of the metadata file, and provides a dict-like interface to the values:
>>> from distutils2.metadata import DistributionMetadata

 >>> metadata = DistributionMetadata('PKG-INFO')

 >>> metadata.keys()[:5]

 ('Metadata-Version', 'Name', 'Version', 'Platform', 'Supported-Platform')

 >>> metadata['Name']

 'CLVault'

 >>> metadata['Version']

 '0.5'

 >>> metadata['Requires-Dist']

 ["pywin32; sys.platform == 'win32'", "Sphinx"]

The fields that supports environment markers can be automatically ignored if the object is instanciated using the platform_dependant option. DistributionMetadata will interpret in the case the markers and willautomatically remove the fields that are not compliant with the running environment.

Here's an example under Mac OS X. The win32 dependency we saw earlier is ignored:
>>> from distutils2.metadata import DistributionMetadata

 >>> metadata = DistributionMetadata('PKG-INFO', platform_dependant=True)

 >>> metadata['Requires-Dist']

 ['Sphinx']

If you want to provide your own execution context, let's say to test the Metadata under a particular environment that is not the current environment, you can provide your own values in the execution_context option, which
is the dict that may contain one or more keys of the context the micro-language expects.

Here's an example, simulating a win32 environment:
>>> from distutils2.metadata import DistributionMetadata

 >>> context = {'sys.platform': 'win32'}

 >>> metadata = DistributionMetadata('PKG-INFO', platform_dependant=True,

 ...                                 execution_context=context)

 ...

 >>> metadata['Requires-Dist'] = ["pywin32; sys.platform == 'win32'",

 ...                              "Sphinx"]

 ...

 >>> metadata['Requires-Dist']

 ['pywin32', 'Sphinx']

Writing metadata

Writing metadata can be done using the write method:

metadata.write('/to/my/PKG-INFO')

The class will pick the best version for the metadata, depending on the values provided. If all the values provided exists in all versions, the class will used metadata.PKG_INFO_PREFERRED_VERSION. It is set by default to "1.0".

Conflict checking and best version

Some fields in PEP 345 have to follow a version scheme in their versions predicate. When the scheme is violated, a warning is emited:

from distutils2.metadata import DistributionMetadata

>>> metadata = DistributionMetadata()

>>> metadata['Requires-Dist'] = ['Funky (Groovie)']

"Funky (Groovie)" is not a valid predicate

>>> metadata['Requires-Dist'] = ['Funky (1.2)']

Stay tuned for some more fortastes of Distutils2 !

And if you want to contribute, join us in #distutils (freenode)

Comments !