`zodbpickle` README

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This package presents a uniform pickling interface for ZODB:

Under Python2, this package forks both Python 2.7's pickle and
cPickle modules, adding support for the protocol 3 opcodes.
It also provides a new subclass of bytes, zodbpickle.binary,
which Python2 applications can use to pickle binary values such that
they will be unpickled as bytes under Py3k.
Under Py3k, this package forks the pickle module (and the supporting
C extension) from both Python 3.2 and Python 3.3. The fork add support
for the noload operations used by ZODB.

Caution

zodbpickle relies on Python's pickle module.
The pickle module is not intended to be secure against erroneous or
maliciously constructed data. Never unpickle data received from an
untrusted or unauthenticated source as arbitrary code might be executed.

Also see https://docs.python.org/3.6/library/pickle.html

General Usage

To get compatibility between Python 2 and 3 pickling, replace::

import pickle

by::

from zodbpickle import pickle

This provides compatibility, but has the effect that you get the fast implementation
in Python 3, while Python 2 uses the slow version.

To get a more deterministic choice of the implementation, use one of::

from zodbpickle import fastpickle # always C
from zodbpickle import slowpickle # always Python

Both modules can co-exist which is helpful for comparison.

But there is a bit more to consider, so please read on!

Loading/Storing Python 2 Strings

In all their wisdom, the Python developers have decided that Python 2 str
instances should be loaded as Python 3 str objects (i.e. unicode
strings). Patches were proposed in Python issue 6784__ but were never
applied. This code base contains those patches.

.. __: http://bugs.python.org/issue6784

Example 1: Loading Python 2 pickles on Python 3 ::

$ python2
>>> import pickle
>>> pickle.dumps('\xff', protocol=0)
"S'\\xff'\np0\n."
>>> pickle.dumps('\xff', protocol=1)
'U\x01\xffq\x00.'
>>> pickle.dumps('\xff', protocol=2)
'\x80\x02U\x01\xffq\x00.'

$ python3
>>> from zodbpickle import pickle
>>> pickle.loads(b"S'\\xff'\np0\n.", encoding='bytes')
b'\xff'
>>> pickle.loads(b'U\x01\xffq\x00.', encoding='bytes')
b'\xff'
>>> pickle.loads(b'\x80\x02U\x01\xffq\x00.', encoding='bytes')
b'\xff'

Example 2: Loading Python 3 pickles on Python 2 ::

$ python3
>>> from zodbpickle import pickle
>>> pickle.dumps(b"\xff", protocol=0)
b'c_codecs\nencode\np0\n(V\xff\np1\nVlatin1\np2\ntp3\nRp4\n.'
>>> pickle.dumps(b"\xff", protocol=1)
b'c_codecs\nencode\nq\x00(X\x02\x00\x00\x00\xc3\xbfq\x01X\x06\x00\x00\x00latin1q\x02tq\x03Rq\x04.'
>>> pickle.dumps(b"\xff", protocol=2)
b'\x80\x02c_codecs\nencode\nq\x00X\x02\x00\x00\x00\xc3\xbfq\x01X\x06\x00\x00\x00latin1q\x02\x86q\x03Rq\x04.'

$ python2
>>> import pickle
>>> pickle.loads('c_codecs\nencode\np0\n(V\xff\np1\nVlatin1\np2\ntp3\nRp4\n.')
'\xff'
>>> pickle.loads('c_codecs\nencode\nq\x00(X\x02\x00\x00\x00\xc3\xbfq\x01X\x06\x00\x00\x00latin1q\x02tq\x03Rq\x04.')
'\xff'
>>> pickle.loads('\x80\x02c_codecs\nencode\nq\x00X\x02\x00\x00\x00\xc3\xbfq\x01X\x06\x00\x00\x00latin1q\x02\x86q\x03Rq\x04.')
'\xff'

Example 3: everything breaks down ::

$ python2
>>> class Foo(object):
...     def __init__(self):
...         self.x = 'hello'
...
>>> import pickle
>>> pickle.dumps(Foo(), protocol=0)
"ccopy_reg\n_reconstructor\np0\n(c__main__\nFoo\np1\nc__builtin__\nobject\np2\nNtp3\nRp4\n(dp5\nS'x'\np6\nS'hello'\np7\nsb."
>>> pickle.dumps(Foo(), protocol=1)
'ccopy_reg\n_reconstructor\nq\x00(c__main__\nFoo\nq\x01c__builtin__\nobject\nq\x02Ntq\x03Rq\x04}q\x05U\x01xq\x06U\x05helloq\x07sb.'
>>> pickle.dumps(Foo(), protocol=2)
'\x80\x02c__main__\nFoo\nq\x00)\x81q\x01}q\x02U\x01xq\x03U\x05helloq\x04sb.'

$ python3
>>> from zodbpickle import pickle
>>> class Foo(object): pass
...
>>> foo = pickle.loads("ccopy_reg\n_reconstructor\np0\n(c__main__\nFoo\np1\nc__builtin__\nobject\np2\nNtp3\nRp4\n(dp5\nS'x'\np6\nS'hello'\np7\nsb.", encoding='bytes')
>>> foo.x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Foo' object has no attribute 'x'

wait what? ::

>>> foo.__dict__
{b'x': b'hello'}

oooh. So we use encoding='ASCII' (the default) and errors='bytes' and
hope it works::

>>> foo = pickle.loads("ccopy_reg\n_reconstructor\np0\n(c__main__\nFoo\np1\nc__builtin__\nobject\np2\nNtp3\nRp4\n(dp5\nS'x'\np6\nS'hello'\np7\nsb.", errors='bytes')
>>> foo.x
'hello'

falling back to bytes if necessary ::

>>> pickle.loads(b'\x80\x02U\x01\xffq\x00.', errors='bytes')
b'\xff'

Support for `noload()`

The ZODB uses cPickle's noload() method to retrieve all persistent
references from a pickle without loading any objects. This feature was removed
from Python 3's pickle. Unfortuantely, this unnecessarily fills the pickle
cache.

This module provides a noload() method again.

===========
Changelog

4.2 (2025-02-12)

Drop support for Python 3.8.
Add preliminary support for Python 3.14 as of 3.14a4.
Remove unused setuptools install requirement.

4.1.1 (2024-10-02)

Fix NameError which occurred when importing zodbpickle.fastpickle.

4.1 (2024-09-17)

Add final support for Python 3.13.

4.0 (2024-05-30)

Drop support for Python 3.7.

3.3 (2024-04-16)

Build Windows wheels on GHA.
Add preliminary support for Python 3.13 as of 3.13a5.

3.2 (2024-02-16)

Add preliminary support for Python 3.13 as of 3.13a3.

3.1 (2023-10-05)

Add support for Python 3.12.

3.0.1 (2023-03-28)

Fix NameError in .fastpickle and .slowpickle.

3.0 (2023-03-24)

Build Linux binary wheels for Python 3.11.
Add preliminary support for Python 3.12a5.
Drop support for Python 2.7, 3.5, 3.6.
Drop support for deprecated python setup.py test.

2.6 (2022-11-17)

Add support for building arm64 wheels on macOS.

2.5 (2022-11-03)

Add support for the final Python 3.11 release.

2.4 (2022-09-15)

Add support for Python 3.11 (as of 3.11.0b3).
Disable unsafe math optimizations in C code. See pull request 73 <https://github.com/zopefoundation/zodbpickle/pull/73>_.

2.3 (2022-04-22)

Add support for Python 3.11 (as of 3.11.0a7).

2.2.0 (2021-09-29)

Add support for Python 3.10.

2.1.0 (2021-09-24)

Add support for Python 3.9.

2.0.0 (2019-11-13)

CPython 2: Make zodbpickle.binary objects smaller and untracked
by the garbage collector. Now they behave more like the native bytes
object. Just like it, and just like on Python 3, they cannot have
arbitrary attributes or be weakly referenced. See issue 53 <https://github.com/zopefoundation/zodbpickle/issues/53>_.

1.1 (2019-11-09)

Add support for Python 3.8.
Drop support for Python 3.4.

1.0.4 (2019-06-12)

Fix pickle corruption under certain conditions. See pull request 47 <https://github.com/zopefoundation/zodbpickle/pull/47>_.

1.0.3 (2018-12-18)

Fix a bug: zodbpickle.slowpickle assigned _Pickler to Unpickler.

1.0.2 (2018-08-10)

Add support for Python 3.7.

1.0.1 (2018-05-16)

Fix a memory leak in pickle protocol 3 under Python 2. See issue 36 <https://github.com/zopefoundation/zodbpickle/issues/36>_.

1.0 (2018-02-09)

Add a warning to the readme not to use untrusted pickles.
Drop support for Python 3.3.

0.7.0 (2017-09-22)

Drop support for Python 2.6 and 3.2.
Add support for Jython 2.7.
Add support for Python 3.5 and 3.6.

0.6.0 (2015-04-02)

Restore the noload behaviour from Python 2.6 and provide the
noload method on the non-C-accelerated unpicklers under PyPy and
Python 2.
Add support for PyPy, PyPy3, and Python 3.4.

0.5.2 (2013-08-17)

Import accelerator from our extension module under Py3k.
See https://github.com/zopefoundation/zodbpickle/issues/6,
https://github.com/zopefoundation/zodbpickle/issues/7.
Fix unpickler's load_short_binstring across supported platforms.

0.5.1 (2013-07-06)

Update all code and tests to Python 2.6.8, 2.7.5, 3.2.5, 3.3.2 .
Add the modules zodbpickle.fastpickle and zodbpickle.slowpickle.
This provides a version-independent choice of the C or Python
implementation.
Fix a minor bug on OS X

0.5.0 (2013-06-14)

Removed support for the bytes_as_strings arguments to pickling APIs:
the pickles created when that argument was true might not be unpickled
without passing encoding='bytes', which ZODB couldn't reliably enforce.
On Py3k, ZODB will be using protocol=3 pickles anyway.

0.4.4 (2013-06-07)

Add protocol 3 opcodes to the C version of the noload() dispatcher.

0.4.3 (2013-06-07)

Packaging error: remove spurious -ASIDE file from sdist.

0.4.2 (2013-06-07)

Fix NameError in pure-Python version of Unpickler.noload_appends.
Fix NameError in pure-Python version of Unpickler.noload_setitems.

0.4.1 (2013-04-29)

Fix typo in Python2 version of zodbpickle.pickle module.

0.4 (2013-04-28)

Support the common pickle module interface for Python 2.6, 2.7, 3.2, and 3.3.
Split the Python implementations / tests into Python2- and Py3k-specific
variants.
Added a fork of the Python 2.7 _pickle.c, for use under Python2.
The fork adds support for the Py3k protocol 3 opcodes.
Added a custom binary type for use in Python2 apps.
Derived from bytes, the binary type allows Python2 apps to pickle
binary data using opcodes which will cause it to be unpickled as bytes
on Py3k. Under Py3k, the binary type is just an alias for bytes.

0.3 (2013-03-18)

Added noload code to Python 3.2 version of Unpickler. As with
the Python 3.3 version, this code remains untested.
Added bytes_as_strings option to the Python 3.2 version of
Pickler, dump, and dumps.

0.2 (2013-03-05)

Added bytes_as_strings option to Pickler, dump, and dumps.
Incomplete support for Python 3.2:
- Move _pickle.c -> _pickle_33.c.
- Clone Python 3.2.3's _pickle.c -> _pickle_32.c and apply the
  same patch.
- Choose between them at build time based on sys.version_info.
- Disable some tests of 3.3-only features.
- Missing: implementation of noload() in _pickle_32.c.
- Missing: implementation of bytes_as_strings=True in _pickle_32.c.

0.1.0 (2013-02-27)

Initial release of Python 3.3's pickle with the patches of Python
issue 6784__ applied.

.. __: http://bugs.python.org/issue6784#msg156166

Added support for errors="bytes".

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