如何使用“pickle”

Question

我的代码（我无法使用“pickle”）：

class A(object):
    def __getstate__(self):
        print 'www'
        return 'sss'
    def __setstate__(self,d):
        print 'aaaa'

import pickle
a = A()
s = pickle.dumps(a)
e = pickle.loads(s)
print s,e

打印：

www
aaaa
ccopy_reg
_reconstructor
p0
(c__main__
A
p1
c__builtin__
object
p2
Ntp3
Rp4
S'sss'
p5
b. <__main__.A object at 0x00B08CF0>

谁可以告诉我如何使用。

Answer 1

你想做什么？它对我有用：

class A(object):
    def __init__(self):
        self.val = 100

    def __str__(self):
        """What a looks like if your print it"""
        return 'A:'+str(self.val)

import pickle
a = A()
a_pickled = pickle.dumps(a)
a.val = 200
a2 = pickle.loads(a_pickled)
print 'the original a'
print a
print # newline
print 'a2 - a clone of a before we changed the value'
print a2
print 

print 'Why are you trying to use __setstate__, not __init__?'
print

所以这将打印：

the original a
A:200

a2 - a clone of a before we changed the value
A:100

如果您需要 setstate：

class B(object):
    def __init__(self):
        print 'Perhaps __init__ must not happen twice?'
        print
        self.val = 100

    def __str__(self):
        """What a looks like if your print it"""
        return 'B:'+str(self.val)

    def __getstate__(self):
        return self.val

    def __setstate__(self,val):
        self.val = val

b = B()
b_pickled = pickle.dumps(b)
b.val = 200
b2 = pickle.loads(b_pickled)
print 'the original b'
print b
print # newline
print 'b2 - b clone of b before we changed the value'
print b2

打印：

Why are you trying to use __setstate__, not __init__?

Perhaps __init__ must not happen twice?

the original b
B:200

b2 - b clone of b before we changed the value
B:100

Answer 2

您可以pickle（意思是，此代码按其应有的方式工作）。你似乎得到了一个结果，但你没有想到。如果您期望相同的“输出”，请尝试：

import pickle
a = A()
s = pickle.dumps(a)
e = pickle.loads(s)
print s, pickle.dumps(e)

您的示例不是典型的“pickling”示例。通常，腌制的对象会永久保存在某个地方或通过网络发送。参见例如 pickletest.py：http://www.sthurlow.com/ python/lesson10/.

pickling 有一些高级用法，请参阅 David Mertz XML 对象序列化文章：http://www.ibm.com/developerworks/xml/library/x-matters11.html

Answer 3

简而言之，在您的示例中，e 等于 a。

不必关心这些奇怪的字符串，您可以转储这些字符串以保存到任何地方，只要记住当您加载它们时，您又得到了“a”对象。