At 02:31 AM 3/22/2008 +0100, Martin v. Löwis wrote:
I'm making the assumption that the author(s) of PEP 262 had good reason for including what they did, rather than assuming that we should start the entire process over from scratch.
The objections to the PEP remain the same as they were then, though: In the requirements, it says "we need", without saying why we need. It then goes on saying "we want" (rephrased) "to duplicate APT and RPM", without saying why we want that, or why that brings us closer to what we need.
IOW, the PEP is lacking a rationale.
Ok, well, I have a rationale for it: make it possible to get rid of eggs as a mechanism for supporting easy_install. Many people (yourself included) have criticized eggs as an installation mechanism, and this is an alternative that gets rid of .egg files and directories in that case, and most of the need for .pth file usage as well.
If there was a chance that the infrastructure being developed actually helps these tools, *that* would be a reasonable goal, IMO.
Yes, I'm of course primarily interested in Python-specific tools such as virtualenv, easy_install, buildout, and the as-yet-unwritten uninstallers, package listers, etc., that can usefully read or write such data.
However, I'm extremely skeptical that this can ever succeed to the degree that whoever provides RPMs, .debs, or MSI files will actually use such data, as they will find that the data are incomplete, and they have to redo all of it, anyway.
The data isn't for them to use to meet their use cases, it's for them to *provide* so that Python tools don't stomp on, uninstall, or otherwise interfere with files installed by the system. In other words, for system packagers, it's a communication from the system to Python, rather than the other way around. Even though the distutils will build the file in the bdist, the system packaging tools would be free to generate their own file listing and signatures and such.
Do you also envision the objective of PEP 262, then? I.e. to provide a database of installed packages, in .../install-db?
In each directory relative to a given sys.path directory, yes. That is, installing a distutils distribution to any directory would result in a file being added to an install-db within that directory. (Assuming we use the proposed implementation model of PEP 262, which at the moment I don't see any substantial obstacle to.)
And as I said, I'll be happy if all we do is get the distutils to abide by the spec for 2.6, even if it means we don't get an uninstall tool. That can always be installed later using Guido's bootstrap tool. :)
I'm even more skeptical here. If the assumption is that the package database allows for uninstallation, I'm -1. IOW, RPM, deb, MSI should then *not* write to that package database, as they also write to a different database, out of the scope of the PEP, and this is what uninstallation should use.
I probably should have brought this up, in fact, I think I mentioned it in a previous thread, but I would like to see PEP 262 add a way to say "this is a system-installed package, *don't touch*". The idea again is not to do the job of the native packaging system, but rather to ensure that Python-specific tools (e.g. easy_install and friends) do not interfere or conflict with it. A big problem in the early development of easy_install, even using eggs, was that there was no way to tell whether it was safe to delete or overwrite an existing file or directory that was already installed on the system. A mechanism like this would allow tools like easy_install to say, "oh, your system packager has a conflicting package here, you need to use that tool to sort this out if you really want to do something here. I'm not going to touch that." Without something like this, there is no way to tell the difference on many systems between a system package and something the user has put there with "sudo python setup.py install".