Ian Bicking wrote:
After setting that project aside someone else at TOPP (Luke Tucker)
did a buildout for Deliverance because we needed to build some
non-Python libraries and that was a feature of buildout; that did end up
working eventually (after considerable effort), but it was not a very
satisfying experience, and *using* the buildout was itself a real
challenge. Since Deliverance is just a library, to do anything useful I
also had to install another package that *uses* that library, and that
was surprisingly difficult. Actually developing those libraries was
even more frustrating.
To my mind, using buildout to manage libraries like that is not what
it's meant for (certainly not where I'd reach for it). Why isn't
deliverance just an egg with its own dependencies?
Buildout to me is a way of setting up my zope instance (which is not an
egg, but a bundle of software) and pulling in the necessary eggs and
products and configuration in a repeatable and mangable way. It's also
fairly open-ended, so that I could make extensions to the process of
setting it all up specific to my use case (by making a new recipie and
wiring it into buildout.cfg, which is as simple as writing a new egg
with an entry point and a single class from what I've seen so far).
So then Rob decides to devote some time to deployment. And because Rob
just wants to get this finished, he wrote the whole things from scratch.
You can see the result of that here:
https://svn.openplans.org/svn/topp.deploy/trunk -- it's not a generic
setup tool, just what works for us. The end result is something that
does everything we want, that we understand, and that we'll understand
how to extend. An important difference from zc.buildout is that all the
logic and work is in *our* script, not in a framework driven by a config
file.
I think this is fine for your own needs. But consider that we want to
document how people should set up their Plone development environment.
If that involves "first, write a shell script that sets it all up, a bit
like so, but tailored to your own needs" then that's pretty much a dead
end for a large number of people who just want to Get Things Done.
At least with ploneout as it is now, you run two commands (boostrap,
then buildout) and you have a fully functional Plone 3 site configured
and you have something you can extend (in ways that are quite obvious to
me, at least) for your own projects.
However, you *didn't* have ploneout, and I suspect that starting from
the zc.* recipes for Zope 3 would've been frustrating. I also suspect
that trying to solve the topp.* problem without a generic Plone version
to build on would've been difficult.
The deployment script also uses workingenv, somewhat similarly because
it is more library-like. Well, also because I work at TOPP and can
easily support their use, which is certainly a nontrivial reason for the
choice. Workingenv in this case is basically a tool that provides the
isolation that we need to create something repeatable. This is the main
feature overlap with buildout. Workingenv is not the framework in which
topp.deploy is written, and workingenv is not intended as a framework.
Indeed, and this is an important distinction.
Note also that topp.deploy does not have the full set of features we'll
ultimately need. You can't tell it to install another egg, or setup
another script, or whatever. And we don't *have* to add those features,
because workingenv is compatible with all the other tools. Where "all
the other" is mostly easy_install. But someday there will be more, even
if the progress is slow. buildout is basically incompatible with
easy_install (the script). And frankly I like easy_install. It's
probably 10x faster than buildout.
I think buildout is mostly slow (at least from ploneout experience)
because some of the generalisations are a bit optimistic. For example,
the current zope 2 recipie tries to check it all out from svn, which
takes forever. I plan to fix that quickly. When I run it in offline
mode, it takes seconds here at least.
easy_install is what people use in
documentation, and its conventions are the ones people know (why does
buildout not use "Pkg==version", for instance?).
No idea, and good point.
I also think it's true that people document easy_install. However,
easy_install is inherently "global" (it deals with a global
site-packages). workingenv "localises" this so that it tricks
easy_install into thinking the instance-specific setup is the global
one. It does so by fiddling environment variables. It is stateful in
that you need to activate and deactivate it. To me, this is less elegant
in relation to the use case of managing a particular project (what if I
forget to activate and then easy_install and accidentally upgrade
something...) than having a well-defined single file that explains what
this project is.
To some extent, working on Zope 2 projects is a bit different from
working in a plain-python environment. Zope has the notion of instances
with separate config files, start/stop scripts and datastore files. It's
not just a script you write that sits in a package and has some
dependencies. Maybe I'm blinded, though.
As for the technical reasons they don't work together:
* workingenv allows and leaves it to setuptools to maintain the package
installation database (basically easy-install.pth). This is not a very
good database, but eh. buildout doesn't really have a database, but
instead just enforces what buildout.cfg indicates.
>
* workingenv relies on that database to give default versions and to
setup the Python path. The fixup it does of installed scripts is fairly
minimal, just setting up sys.path enough to force its site.py to get
called. buildout enumerates all the activated packages, and ignores
easy-install.pth. This is basically what makes it
easy_install-incompatible. Plus buildout's desire to own everything and
destroy everything it does not own ;)
That is somewhat down to recipes, though. I certainly want to tie this
down in the zope 2 recipies to be less destructive (we're already almost
there).
* As a result buildout supports multiple things in the same buildout
that have conflicting version requirements, but where the packages
themselves don't realize this (but the deployer does). If the packages
know their requirements then setuptools' native machinery allows things
to work fine. The solution with workingenv is to create multiple
environments. Since the actual building happens higher up (e.g.,
topp.deploy), there's nothing stopping you from creating multiple
environments from one deployment script. Anyway, in summary the way
scripts are generated is one of the major incompatibilities between
buildout and workingenv. In effect Buildout's jail is too strong for
workingenv to penetrate, and buildout doesn't tell anyone else about
what it is doing.
* workingenv allows you to change versions without informing or using
workingenv. Once you've created the environment you mostly stop using
workingenv directly.
* Some see bin/activate as a jail. Both workingenv and buildout are
deliberately jail-like. Both Jim and I loathe the non-repeatability of
system-wide installations (at least I think I can speak for him on that
one point ;). bin/activate lets you into that jail, and lets you work
there. There is no way into a buildout. Frankly this weirds me out,
and is a big part of my past frustration with it. Maybe that's because
I'm in the relatively uncommon situation that I actually know what's
going on under the hood of Python imports and packaging, and so it
bothers me that I can't debug things directly.
Probably. I think it also has something to do with the fact that Zope
people (me included) think in the context of a Zope instance as the
ultimate controller of what gets executed. The buildout builds an
instance plus some other stuff and informs it of what packages it has
available.
Anyway, neither requires
activation when using scripts generated in the environment. And
bin/activate is really just something that sets PYTHONPATH and then does
other non-essential things like changing the prompt and $PATH -- I
should probably document that more clearly. Neither can be entirely
compatible with a system-wide Python installation, because Python's
standard site.py f**ks up the environment really early in the process,
and avoiding that isn't all that easy. In some ways virtual-python is
the more complete solution to all of this, and sometimes I think I
should just use that technique (of a separate Python interpreter, and
hence separate prefix) with some of the improvements I could take from
workingenv.
Anyway, this is my very long summary of why we aren't using buildout,
and are using workingenv.
I am still trying to learn more about the details of how eggs and
dependency management work. You certainly understand it better than me,
and I found some of this quite enlightening. I would love it if Jim or
someone more involved in the original design of zc.buildout had anything
to add in answer to your specific points above. :)
Martin
_______________________________________________
Zope-Dev maillist - [email protected]
http://mail.zope.org/mailman/listinfo/zope-dev
** No cross posts or HTML encoding! **
(Related lists -
http://mail.zope.org/mailman/listinfo/zope-announce
http://mail.zope.org/mailman/listinfo/zope )
