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|
Pickling Persistent Objects
===========================
Persistent objects are designed to make the standard Python pickling
machinery happy:
.. doctest::
>>> import pickle
>>> from persistent.tests.cucumbers import Simple
>>> from persistent.tests.cucumbers import print_dict
>>> x = Simple('x', aaa=1, bbb='foo')
>>> print_dict(x.__getstate__())
{'__name__': 'x', 'aaa': 1, 'bbb': 'foo'}
>>> f, (c,), state = x.__reduce__()
>>> f.__name__
'__newobj__'
>>> f.__module__
'copy_reg'
>>> c.__name__
'Simple'
>>> print_dict(state)
{'__name__': 'x', 'aaa': 1, 'bbb': 'foo'}
>>> import pickle
>>> pickle.loads(pickle.dumps(x)) == x
True
>>> pickle.loads(pickle.dumps(x, 0)) == x
True
>>> pickle.loads(pickle.dumps(x, 1)) == x
True
>>> pickle.loads(pickle.dumps(x, 2)) == x
True
>>> x.__setstate__({'z': 1})
>>> x.__dict__
{'z': 1}
This support even works well for derived classes which customize pickling
by overriding :meth:`__getnewargs__`, :meth:`__getstate__` and
:meth:`__setstate__`.
.. doctest::
>>> from persistent.tests.cucumbers import Custom
>>> x = Custom('x', 'y')
>>> x.__getnewargs__()
('x', 'y')
>>> x.a = 99
>>> (f, (c, ax, ay), a) = x.__reduce__()
>>> f.__name__
'__newobj__'
>>> f.__module__
'copy_reg'
>>> c.__name__
'Custom'
>>> ax, ay, a
('x', 'y', 99)
>>> pickle.loads(pickle.dumps(x)) == x
True
>>> pickle.loads(pickle.dumps(x, 0)) == x
True
>>> pickle.loads(pickle.dumps(x, 1)) == x
True
>>> pickle.loads(pickle.dumps(x, 2)) == x
True
The support works for derived classes which define :attr:`__slots__`. It
ignores any slots which map onto the "persistent" namespace (prefixed with
``_p_``) or the "volatile" namespace (prefixed with ``_v_``):
.. doctest::
>>> import copy_reg
>>> from persistent.tests.cucumbers import SubSlotted
>>> x = SubSlotted('x', 'y', 'z')
Note that we haven't yet assiged a value to the ``s4`` attribute:
.. doctest::
>>> d, s = x.__getstate__()
>>> d
>>> print_dict(s)
{'s1': 'x', 's2': 'y', 's3': 'z'}
>>> import pickle
>>> pickle.loads(pickle.dumps(x)) == x
True
>>> pickle.loads(pickle.dumps(x, 0)) == x
True
>>> pickle.loads(pickle.dumps(x, 1)) == x
True
>>> pickle.loads(pickle.dumps(x, 2)) == x
True
After assigning it:
.. doctest::
>>> x.s4 = 'spam'
>>> d, s = x.__getstate__()
>>> d
>>> print_dict(s)
{'s1': 'x', 's2': 'y', 's3': 'z', 's4': 'spam'}
>>> pickle.loads(pickle.dumps(x)) == x
True
>>> pickle.loads(pickle.dumps(x, 0)) == x
True
>>> pickle.loads(pickle.dumps(x, 1)) == x
True
>>> pickle.loads(pickle.dumps(x, 2)) == x
True
:class:`persistent.Persistent` supports derived classes which have base
classes defining :attr:`__slots`, but which do not define attr:`__slots__`
themselves:
.. doctest::
>>> from persistent.tests.cucumbers import SubSubSlotted
>>> x = SubSubSlotted('x', 'y', 'z')
>>> d, s = x.__getstate__()
>>> print_dict(d)
{}
>>> print_dict(s)
{'s1': 'x', 's2': 'y', 's3': 'z'}
>>> import pickle
>>> pickle.loads(pickle.dumps(x)) == x
True
>>> pickle.loads(pickle.dumps(x, 0)) == x
True
>>> pickle.loads(pickle.dumps(x, 1)) == x
True
>>> pickle.loads(pickle.dumps(x, 2)) == x
True
>>> x.s4 = 'spam'
>>> x.foo = 'bar'
>>> x.baz = 'bam'
>>> d, s = x.__getstate__()
>>> print_dict(d)
{'baz': 'bam', 'foo': 'bar'}
>>> print_dict(s)
{'s1': 'x', 's2': 'y', 's3': 'z', 's4': 'spam'}
>>> pickle.loads(pickle.dumps(x)) == x
True
>>> pickle.loads(pickle.dumps(x, 0)) == x
True
>>> pickle.loads(pickle.dumps(x, 1)) == x
True
>>> pickle.loads(pickle.dumps(x, 2)) == x
True
|
