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Issue #17810: Implement PEP 3154, pickle protocol 4.

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Most of the work is by Alexandre.
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Antoine Pitrou 2013-11-23 18:59:12 +01:00
parent 95401c5f6b
commit c9dc4a2a8a
12 changed files with 3132 additions and 1006 deletions
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35
Doc/library/pickle.rst
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@ -459,12 +459,29 @@ implementation of this behaviour::
Classes can alter the default behaviour by providing one or several special
methods:
.. method:: object.__getnewargs_ex__()
In protocols 4 and newer, classes that implements the
:meth:`__getnewargs_ex__` method can dictate the values passed to the
:meth:`__new__` method upon unpickling. The method must return a pair
``(args, kwargs)`` where *args* is a tuple of positional arguments
and *kwargs* a dictionary of named arguments for constructing the
object. Those will be passed to the :meth:`__new__` method upon
unpickling.
You should implement this method if the :meth:`__new__` method of your
class requires keyword-only arguments. Otherwise, it is recommended for
compatibility to implement :meth:`__getnewargs__`.
.. method:: object.__getnewargs__()
In protocol 2 and newer, classes that implements the :meth:`__getnewargs__`
method can dictate the values passed to the :meth:`__new__` method upon
unpickling. This is often needed for classes whose :meth:`__new__` method
requires arguments.
This method serve a similar purpose as :meth:`__getnewargs_ex__` but
for protocols 2 and newer. It must return a tuple of arguments `args`
which will be passed to the :meth:`__new__` method upon unpickling.
In protocols 4 and newer, :meth:`__getnewargs__` will not be called if
:meth:`__getnewargs_ex__` is defined.
.. method:: object.__getstate__()
@ -496,10 +513,10 @@ the methods :meth:`__getstate__` and :meth:`__setstate__`.
At unpickling time, some methods like :meth:`__getattr__`,
:meth:`__getattribute__`, or :meth:`__setattr__` may be called upon the
instance. In case those methods rely on some internal invariant being true,
the type should implement :meth:`__getnewargs__` to establish such an
invariant; otherwise, neither :meth:`__new__` nor :meth:`__init__` will be
called.
instance. In case those methods rely on some internal invariant being
true, the type should implement :meth:`__getnewargs__` or
:meth:`__getnewargs_ex__` to establish such an invariant; otherwise,
neither :meth:`__new__` nor :meth:`__init__` will be called.
.. index:: pair: copy; protocol
@ -511,7 +528,7 @@ objects. [#]_
Although powerful, implementing :meth:`__reduce__` directly in your classes is
error prone. For this reason, class designers should use the high-level
interface (i.e., :meth:`__getnewargs__`, :meth:`__getstate__` and
interface (i.e., :meth:`__getnewargs_ex__`, :meth:`__getstate__` and
:meth:`__setstate__`) whenever possible. We will show, however, cases where
using :meth:`__reduce__` is the only option or leads to more efficient pickling
or both.