[Distutils] Why are egg-info and related pth files required for rpm packages?
Phillip J. Eby
pje at telecommunity.com
Tue Sep 4 22:04:36 CEST 2007
At 12:39 PM 9/4/2007 -0400, Stanley A. Klein wrote:
>I recently installed Fedora 7 and looked at
>/usr/lib/python2.5/site-packages. The directory has numerous Python
>packages installed but no egg-info and few .pth files. Of the three .pth
>files in my installation, only one has a content different from the name
>of the package (pointing to a subdirectory of site-packages with a
>Setuptools has the advantage of simplifying preparation of rpms because it
>has find_packages(). However, it produces egg-info and .pth files as part
>of the rpm's.
>I can understand the need for these files when packaging into eggs for
>installation in places other than python/site-packages or when packaging
>for non-Linux operating systems. But why are they needed when installing
>as rpms on Linux systems into site-packages?
>I think this issue applies to most Linux packaging, which is usually
>either rpm or deb.
The .egg-info files or directories are required in order to contain
project-level metadata. Without them, the fact that the packages are
installed can't be detected in a cross-platform way, and other
projects *simply won't function without them*. For example, Chandler
i18n support is provided via the contents of .egg-info, as is plugin
registration. A wide range of plugin-supporting libraries and tools
absolutely require .egg-info, including TurboGears, Buffet, Trac,
Chandler and setuptools itself. Setuptools can't even build itself
unless its own .egg-info is present!
So .egg-info is absolutely indispensable, regardless of installation method.
As for .pth files, the only .pth files that should be generated by
setuptools are the ones needed to support namespace packages. When
you have multiple projects spanning a namespace package, each of
those projects would contain "somepackage/__init__.py" in its naive
layout. But this would cause conflicts between the RPMs, so
setuptools uses uniquely-named .pth files to work around the absence
of an __init__.py. So, these "Project-version-nspkg.pth" files are
also indispensable, as the packages involved won't be importable without them.
However, the .pth files you described don't sound like ones generated
Note, by the way, that as of Python 2.5, *all* distutils-generated
packages include .egg-info; they just use a single file instead of a
directory. This makes it easy to detect what Python packages are
installed on a system, as long as the platform maintainers don't
remove this file.
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