[Python-Dev] [Distutils] PEP 365 (Adding the pkg_resources module)

Mon Mar 17 22:19:31 CET 2008

Folks:
(By the way, it was a pleasure to meet many of you in Real Life for 
the first time at Pycon.)
Here is what I want:
1. The standard Python build tools by default produce machine- 
parseable package metadata, which can include package dependency 
information with reasonably well-defined semantics.
Oh good! I already have this, since distutils in Python >= 2.5 
produces .egg-info metadata in an easy-to-parse format.
2. This machine-parseable metadata is widely supported and 
understood by the Python community.
In retrospect, it's too bad that it isn't named ".pkg-info" instead 
of ".egg-info", in order to avoid the fraught politics around the 
concept of "eggs". A concrete example of such a misunderstanding is 
the sad fact that many Linux distributions were in the habit of 
deleting this information from their Python packages, perhaps because 
they were under the impression that it was obviated by their 
packaging tools. The major distributions have all stopped doing this 
now.
Unifying the created-by-default PKG-INFO files and the created-by- 
default .egg-info directories would be nice, too.
3. The standard Python library includes a tool to find and parse 
this metadata, so that I can write programmatic tests of my 
dependencies, like this:
http://allmydata.org/trac/tahoe/browser/_auto_deps.py?rev=2062
This is one of the improvements that I was anticipating from 
pkg_resources going into the standard library.
4. The standard Python library includes a tool to find and read 
resources (other than Python modules) that came bundled in a Python 
package.
Consider, for example, this snippets of code in Nevow:
http://divmod.org/trac/browser/trunk/Nevow/setup.py?rev=13786#L10
http://divmod.org/trac/browser/trunk/Nevow/setup.py?rev=13786
http://divmod.org/trac/browser/trunk/Nevow/setup_egg.py?rev=2406
When Nevow uses pkg_resources to import its files such as 
"default.css", then it is able to find at runtime, even if is being 
imported from a py2exe or py2app zip, or on other platforms where its 
homegrown setup script and homegrown "find my file" function fail. 
So using pkg_resources (and setuptools to install it) makes 
"test_nevow" pass on all of the allmydata.org buildslaves:
http://allmydata.org/buildbot/waterfall?show_events=false
Regards,
Zooko