import cPickle
class Foo(object):
def __init__(self):
self._data = {'bar': 'baz'}
def __getattr__(self, name):
assert hasattr(self, '_data')
return self._data[name]
# I even had to define this just to stop KeyError: '__getstate__'
def __getstate__(self):
return self.__dict__
foo = Foo()
bar = cPickle.dumps(foo)
cPickle.loads(bar)
这引发了断言错误.
我认为pickle / cPickle在转储时只是将__dict__变成一个字符串,然后在加载时直接使用该字符串来设置新对象的__dict__.为什么转储需要调用bar .__ getattr__?我怎样才能改变Foo以避免这种情况?
最佳答案 根据cPickle:
http://docs.python.org/library/pickle.html的文档
object.__getstate__()
Classes can further influence how their instances are pickled; if the class defines the method
__getstate__()
, it is called and the return state is pickled as the contents for the instance, instead of the contents of the instance’s dictionary. If there is no__getstate__()
method, the instance’s__dict__
is pickled.Note
At unpickling time, some methods like
__getattr__()
,
__getattribute__()
, or__setattr__()
may be called upon the instance. In case those methods rely on some internal invariant being true, the
type should implement either__getinitargs__()
or__getnewargs__()
to
establish such an invariant; otherwise, neither__new__()
nor
__init__()
will be called.
既然你试图断言hasattr(self,’_ data’)是True,我相信你需要使用__getinitargs __()或__getnewargs __().这是因为在使用pickle时,不会调用类__init__方法.