Python pickle模块用法实例分析
本文实例讲述了Python pickle模块用法。分享给大家供大家参考。具体分析如下：
pickle提供了一个简单的持久化功能。可以将对象以文件的形式存放在磁盘上。
pickle.dump(obj, file[, protocol])
序列化对象，并将结果数据流写入到文件对象中。参数protocol是序列化模式，默认值为0，表示以文本的形式序列化。protocol的值还可以是1或2，表示以二进制的形式序列化。
pickle.load(file)
反序列化对象。将文件中的数据解析为一个Python对象。
其中要注意的是，在load(file)的时候，要让python能够找到类的定义，否则会报错：
比如下面的例子
import pickle
class Person:
def __init__(self,n,a):
self.name=n
self.age=a
def show(self):
print self.name+"_"+str(self.age)
aa = Person("JGood", 2)
aa.show()
f=open('d:\\p.txt','w')
pickle.dump(aa,f,0)
f.close()
#del Person
f=open('d:\\p.txt','r')
bb=pickle.load(f)
f.close()
bb.show()
如果不注释掉del Person的话，那么会报错如下：
>>> JGood_2 Traceback (most recent call last): File "C:/py/test.py", line 15, in <module> bb=pickle.load(f) File "C:\Python27\lib\pickle.py", line 1378, in load return Unpickler(file).load() File "C:\Python27\lib\pickle.py", line 858, in load dispatch[key](self) File "C:\Python27\lib\pickle.py", line 1069, in load_inst klass = self.find_class(module, name) File "C:\Python27\lib\pickle.py", line 1126, in find_class klass = getattr(mod, name) AttributeError: 'module' object has no attribute 'Person'
意思就是当前模块找不到类的定义了。
clear_memo()
清空pickler的“备忘”。使用Pickler实例在序列化对象的时候，它会“记住”已经被序列化的对象引用，所以对同一对象多次调用dump(obj)，pickler不会“傻傻”的去多次序列化。
看下面的例子：
import StringIO
import pickle
class Person:
def __init__(self,n,a):
self.name=n
self.age=a
def show(self):
print self.name+"_"+str(self.age)
aa = Person("JGood", 2)
aa.show()
fle = StringIO.StringIO()
pick = pickle.Pickler(fle)
pick.dump(aa)
val1=fle.getvalue()
print len(val1)
pick.clear_memo()
pick.dump(aa)
val2=fle.getvalue()
print len(val2)
fle.close()
上面的代码运行如下：
>>> JGood_2 66 132 >>>
此时再注释掉pick.clear_memo()后，运行结果如下：
>>> JGood_2 66 70 >>>
主要是因为，python的pickle如果不clear_memo，则不会多次去序列化对象。
希望本文所述对大家的Python程序设计有所帮助。
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