在我的类实例化期间,我初始化一些不可选择的字段.因此,为了能够(un)正确地挑选我的类,我希望我的init方法可以在unpickling上调用.这似乎是它与旧式课程一起使用的方式.
对于新的样式类,我需要使用__new__和__getnewargs__.这是我做的:
import cPickle
class Blubb(object):
def __init__(self, value):
self.value = value
class Bla(Blubb):
def __new__(cls, value):
instance = super(Bla, cls).__new__(cls)
instance.__init__(value)
return instance
def __getnewargs__(self):
return self.value,
def __getstate__(self):
return {}
def __setstate__(self, dct):
pass
x = Bla(2)
print x.value
pickled = cPickle.dumps(x, 2)
x_ = cPickle.loads(pickled)
assert x_.value == 2
如果没有obj = C .__ new __(C,* args)的事实,这将没有问题.现在有** kwargs.所以我在__new__和__init__方法中仅限于非关键字参数.
有谁知道解决这个问题的方法?这真的很不方便.
最佳答案 pickle协议2默认调用cls .__ new __(cls,* args),但有一种解决方法.如果使用__reduce__,则可以返回一个函数,该函数将您的参数映射到__new__.我能够修改你的例子让** kwargs工作:
import cPickle
class Blubb(object):
def __init__(self, value, foo=None, bar=None):
self.value = value
self.foo = foo
self.bar = bar
def _new_Bla(cls, value, kw):
"A function to map kwargs into cls.__new__"
return cls.__new__(cls, value, **kw)
class Bla(Blubb):
def __new__(cls, value, **kw):
instance = super(Bla, cls).__new__(cls)
instance.__init__(value, **kw)
return instance
def __reduce__(self):
kwargs = {'foo': self.foo, 'bar': self.bar}
return _new_Bla, (self.__class__, self.value, kwargs), None
x = Bla(2, bar=[1, 2, 3])
pickled = cPickle.dumps(x, 2)
y = cPickle.loads(pickled)
assert y.value == 2
assert y.bar == [1, 2, 3]