[Announce] Major update to the xml_pickle package

[frankm at hiwaay.net]

Hi, I just wanted to send a note to announce a rather large
update to the xml_pickle package. I started with xml_pickle-0.51
and (together with David Mertz) added a bunch of things to make
xml_pickle a functional superset of the standard pickle module.

[Background blurb: xml_pickle is a package that looks, internally
and externally, like the standard pickle module, but produces XML
output using a minimalistic encoding.]

New features, compared to xml_pickle-0.51:

  o Can now fully restore class functionality, just like the
    standard pickle module.

  o Full internal compatibility with the pickle protocol
    (objects with __getstate__,__setstate__, and __getinitargs__
     are pickled/unpickled exactly as pickle does).

  o A pickle-compatible API layer
    (xml_pickle.dump()/dumps()/load()/loads() are drop-in compatible
     with the standard pickle module.)

  o A type-extension "plugin" system allows you to create "pretty
    printed" XML representations of objects if so desired.

  o Virtually all objects that can be pickled can be XML-pickled.
    (The only exception is that builtin types cannot be pickled as
     *toplevel* objects, since they are not true InstanceTypes.
     This restriction may be removed in a future version.)

  o Python 2.2 compatibility (Remains compatible with Python 2.0+)

  o Fine-grained security model added. I consider this an improvement
    over regular pickle, since it allows you to control how classes
    are created during unpickling. This means you can load pickles
    from "untrusted" sources and not worry about what you're getting
    (ie. no one can trick you into loading an EvilList where you
     expected a UserList). See "pydoc gnosis.xml.pickle.doc" for more
     information about the security model.

  o DEEPCOPY option added, so you can choose whether or not to have
    references inserted in the XML stream. References are great for
    saving space, but deepcopying allows third-party/non-Python parsers
    to get the entire data set without having to understand references.

  o References now keep the "pointed-to" type in the XML tag.
    This allows third-party/non-Python parsers to easily tell what the
    referenced object contains without reconstructing the object tree.

  o A few other bugfixes/improvements:
      - Corrected refchecking of temporary objects and key/val/items.
      - Numerical.arrays are now refchecked
      - SREs are now pickled

Given that there are alternative XML encoding schemes (such as XML-RPC
and WDDX), a few words to explain the particular purpose and goals of
xml_pickle seem to be in order:

   o It looks & feels just like the standard pickle module, both
     internally and externally, so all extension classes that
     speak the pickle protocol will "just work".

   o Has a minimalistic encoding scheme. All objects are represented
     using only five tags (<attr>,<entry>,<item>,<key>,and <val>) to
     simplify parsing by third-party/non-Python code.

   o The XML format is rich enough to enable xml_pickle to restore
     objects "fully alive", yet simple enough for "dumb" parsers
     to grab the complete data structures without needing to understand
     anything about Python classes, pickling, etc.

Despite the numerous changes, xml_pickle remains backward compatible
with the xml_pickle-0.51 API (and with XML documents created by older
versions of xml_pickle). The only source-level change you should have
to make would be to change the "import" line, since xml_pickle is now
part of a larger package.

For example:
    import xml_pickle
Could be rewritten:
    import gnosis.xml.pickle as xml_pickle

The complete package (Gnosis_XML_Utils), containing xml_pickle and
other useful components like xml_objectify and xml_indexer, is
released as public domain software, and is available from:

   http://gnosis.cx/download

Specifically (as of this writing):
   http://gnosis.cx/download/Gnosis_XML_Utils-0.9.tar.gz

Given the numerous changes, it'd be great to have as many people as
possible test it. The new package includes a good set of test cases
that also demonstrate the many new features of xml_pickle. Unpack the
sources, and look in gnosis/xml/pickle/test. Run "test_all.py" for a
complete set of tests.

Please send feedback, bug reports, etc., to either myself
(frankm at hiwaay.net) or David Mertz (mertz at gnosis.cx).

(Development was done on Linux and OS/2, so feedback about successes
or failures on other platforms would be greatly appreciated!)

Thanks!
frank

Summary:
<P><A HREF="http://gnosis.cx/download/Gnosis_XML_Util.ANNOUNCE">
Gnosis_XML_Util 0.9</A>
xml_pickle (pickle to XML), xml_objectify and xml_indexer (15-Feb-02)