I've begun work on breaking out the transaction module so it can be used independently from ZODB.

Here's what I've done so far:

- I've moved TransactionError and TransactionFailedError from ZODB.POSException into transaction.interfaces, e.g.:

  class TransactionError(Exception):
      """An error occurred due to normal transaction processing."""

  class TransactionFailedError(Exception):
"""Cannot perform an operation on a transaction that previously failed.

An attempt was made to commit a transaction, or to join a transaction, but this transaction previously raised an exception during an attempt to commit it. The transaction must be explicitly aborted, either by invoking abort() on the transaction, or begin() on its transaction
      manager.
      """

- I've caused ZODB.POSException to add the POSError base class to both TransactionError and TransactionFailedError
  after importing them from transaction.interfaces, e.g.:

  from transaction.interfaces import TransactionError
  from transaction.interfaces import TransactionFailedError

  # We want to be able to distribute the transaction module independent
# from ZODB but we need to maintain backwards compatibility with older
  # ZODB releases, where TransactionError and TransactionFailedError
  # were actually defined within ZODB.POSException, and inherited from
  # POSError.  With this solution, if ZODB is present, TransactionError
  # and TransactionFailedError will have POSError as a base class.  If
  # ZODB is not present, they won't.  Thanks to Ian Bicking for
  # suggesting this solution; as ugly as it is, it does the job.

  TransactionError.__bases__ += (POSError,)
  TransactionFailedError.__bases__ += (POSError,)

- I've created a zc.zodbutils package that is essentially the code that currently lives in the ZODB.utils module; I've also moved the TimeStamp.c code that currently lives in 'persistent' into it. A stub ZODB.utils module exists that just does "from zc.zodbutils import *", and in the persistent package's __init__.py, I
  do "from zc.zodbutils import TimeStamp" for backwards compatibility.

The intention is that the "transaction" distribution will depend only on zc.zodbutils (as will of course the ZODB distro, along with its other current dependencies plus the transaction distribution). I'm wondering about version numbering and naming for the separate packages.. I suspect we shouldn't try to marry the transaction distribution version number to the ZODB distribution version number because they really won't be tied together that way. Maybe just start transaction at "1.0" or something. And I'm thinking that the transaction distribution should be named just "transaction". And the name "zc.zodbutils" is just a placeholder, suggestions from interested parties would be helpful.

I haven't adjusted any imports in tests, nor have I repackaged the transaction module using setuptools yet. I wanted to get a sense of whether folks thought what I've done so far is reasonable or if you might have done it differently.

- C

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