FixupDependencies

Author

JimFulton?

Status

IsProposal?

Problem

ZODB packages are highly interdependent. As things stand now, they might as well be a single package. I don't think this is good. Now that Python has packaging support, I'd like to be able to distribute these in a more fine grained way. In particular:

• It should be possible to use transaction without everything else.
• It should be possible to use ZODB without ZEO,
• It should be possible to use ZODB without any one particular storage.
• It should be possible to use ZODB without BTrees?.
• If anyone ever makes the ifdefs work again, it should be possible to use BTrees? without anything else. It should certainly be possible to use BTrees? without ZODB.
• It should theoretically be possible to use persistent without anything else. This may never be of practical consequence, but I think that the architecture would be cleaner if the dependency wasn't there.

Proposal

I'd like to propose the following dependencies:

persistent

"nothing"

transaction

zope.event

BTrees?

persistent (someday, optionally)

ZODB

transaction, persistent

ZEO

ZODB, transaction

storagex

ZODB

Notes:

• We may have to factor some things out into common dependencies. For example, transaction uses the WeakSet? class defined in ZODB. This class will need to be provided in a separate package. (It could technically move to transaction. Maybe someday, it could move to Python's weakref module.)
• Everything will depend on zope.interface and probably on zope.testing for testing support. The later can be a "test" dependency in setuptools jargon. I expect that zope.deferredimport will become a dependency of many of these packages to avoid circular import problems while allowing names to be made available for convenience at the package level.
• ZConfig? should be an optional dependency of ZODB and ZEO. There should be ZConfig? support included, but it should be possible to use ZODB even if ZConfig? is not installed.
• As with ZConfig?, zdaemon should be an optional dependency of ZEO.
• ThreadedAsync? and ZopeUndo? must go. Nuff said. :)
• Ideally, the storages should become separate packages.

If we agree with this plan, I'd like to start by:

1. Not creating new sources of dependencies. One of the most common ways to create dependencies is by being sloppy in tests. For example, by using ZODB to test transaction.

   I ask that people not write new tests that worsen the dependency situation. Ideally, if you update a test, perhaps you could clean it up.

2. I intend to start with transaction. There is some interest in using transaction outside of ZODB. I think the dependencies are fairly shallow.
   • WeakSet? needs to move. If I'm feeling particularly lazy, I'll just move it to transaction. :)
   • The tests need to be cleaned up so that they don't use ZODB.
   • The exceptions need to be decoupled. I propose to define TransactionFailedError? (possibly with a shorter name) in transaction. This will not extend POSError?. ZODB.TransactionFailedError? will extend the moved error and POSError?.