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()

>>> 
JGood_2

Traceback (most recent call last):
 File "C:/py/test.py", line 15, in <module>
  bb=pickle.load(f)
 File "C:Python27libpickle.py", line 1378, in load
  return Unpickler(file).load()
 File "C:Python27libpickle.py", line 858, in load
  dispatch[key](self)
 File "C:Python27libpickle.py", line 1069, in load_inst
  klass = self.find_class(module, name)
 File "C:Python27libpickle.py", line 1126, in find_class
  klass = getattr(mod, name)
AttributeError: 'module' object has no attribute 'Person'

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()

>>> 
JGood_2
66
132
>>> 

>>> 
JGood_2
66
70
>>>