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Add example for the change to pickle and note the effect of the fix_imports option.

This commit is contained in:
Raymond Hettinger 2009-06-09 21:01:05 +00:00
parent 0803d8713a
commit 662bad868e
1 changed files with 24 additions and 18 deletions
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42
Doc/whatsnew/3.1.rst
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@ -376,6 +376,30 @@ New, Improved, and Deprecated Modules
(Contributed by Derek Morr; :issue:`1655` and :issue:`1664`.)
* The :mod:`pickle` module has been adapted for better interoperability with
Python 2.x when used with protocol 2 or lower. The reorganization of the
standard library changed the formal reference for many objects. For
example, ``__builtin__.set`` in Python 2 is called ``builtins.set`` in Python
3. This change cofounded efforts to share data between different versions of
Python. But now when protocol 2 or lower is selected, the pickler will
automatically use the old Python 2 names for both loading and dumping. This
remapping is turned-on by default but can be disabled with the *fix_imports*
option::
>>> s = {1, 2, 3}
>>> pickle.dumps(s, protocol=0)
b'c__builtin__\nset\np0\n((lp1\nL1L\naL2L\naL3L\natp2\nRp3\n.'
>>> pickle.dumps(s, protocol=0, fix_imports=False)
b'cbuiltins\nset\np0\n((lp1\nL1L\naL2L\naL3L\natp2\nRp3\n.'
An unfortunate but unavoidable side-effect of this change is that protocol 2
pickles produced by Python 3.1 won't be readable with Python 3.0. The latest
pickle protocol, protocol 3, should be used when migrating data between
Python 3.x implementations, as it doesn't attempt to remain compatible with
Python 2.x.
(Contributed by Alexandre Vassalotti and Antoine Pitrou, :issue:`6137`.)
* A new module, :mod:`importlib` was added. It provides a complete, portable,
pure Python reference implementation of the :keyword:`import` statement and its
counterpart, the :func:`__import__` function. It represents a substantial
@ -384,24 +408,6 @@ New, Improved, and Deprecated Modules
(Contributed by Brett Cannon.)
* :mod:`pickle` is now more compatible with Python 2.x when using a
2.x-compatible protocol (that is, protocol 2 or lower), through translation
of some standard library module names to or from their Python 2.x
equivalents.
This means that more (protocol 2 or lower) pickles produced by Python 3.1
will be reusable by Python 2.x, and vice-versa. Standard set objects are
an example of this improvement.
This has the (unfortunate but unavoidable) side effect that some
protocol 2 pickles produced by Python 3.1 won't be readable with
Python 3.0. The latest pickle protocol, protocol 3, should be used when
migrating data between Python 3.x implementations, as it doesn't attempt
to remain compatible with Python 2.x.
(Contributed by Alexandre Vassalotti and Antoine Pitrou, :issue:`6137`.)
Optimizations
=============