pickle使用

>>> import pickle
>>> student_info = {‘name‘:‘peter‘,‘age‘:20}
>>> f = open(‘student.pkl‘,‘w‘)
>>> pickle.dump(student_info,f) #数据保存到文件
>>> f.close()
>>> s = pickle.load(f)  #从文件中读取数据，生成相应的对象
>>> s
{‘age‘: 20, ‘name‘: ‘peter‘}
>>> f.tell()  #加载文件后，文件的读写指针发生了偏移，这是从文件中加载多个对象的基础
45
>>> f.close()


[hupeng@hupeng-vm class]$cat student.pkl 
(dp0
S‘age‘
p1
I20
sS‘name‘
p2
S‘peter‘
p3

>>> student_list = [{‘name‘:‘student_%d‘ %(i)}for i in range(5)]
>>> student_list
[{‘name‘: ‘student_0‘}, {‘name‘: ‘student_1‘}, {‘name‘: ‘student_2‘}, {‘name‘: ‘student_3‘}, {‘name‘: ‘student_4‘}]
>>> f = open(‘students.pkl‘,‘w‘)
>>> for i in range(5):
...     pickle.dump(student_list[i],f)  #逐条写入
... 
>>> f.close()
>>> f = open(‘students.pkl‘,‘r‘)
>>> while True:
...     try:
...         print pickle.load(f)
...         print ‘file offset:‘, f.tell()  #读取一次文件，文件指针发生向后偏移
...     except EOFError: #读到文件结尾
...         break
... 
{‘name‘: ‘student_0‘}
file offset: 34
{‘name‘: ‘student_1‘}
file offset: 68
{‘name‘: ‘student_2‘}
file offset: 102
{‘name‘: ‘student_3‘}
file offset: 136
{‘name‘: ‘student_4‘}
file offset: 170

[hupeng@hupeng-vm class]$cat students.pkl 
(dp0
S‘name‘
p1
S‘student_0‘
p2
s.(dp0
S‘name‘
p1
S‘student_1‘
p2
s.(dp0
S‘name‘
p1
S‘student_2‘
p2
s.(dp0
S‘name‘
p1
S‘student_3‘
p2
s.(dp0
S‘name‘
p1
S‘student_4‘
p2

# coding=utf-8


class MyClass(object):
    def __init__(self):
        self.data = []

    def __str__(self):
        return ‘Custom Class MyClass Data:%s‘ %(self.data)
    
    def add_item(self, item):
        self.data.append(item)

# coding=utf-8
import pickle
import custom_class


obj = custom_class.MyClass()
obj.add_item(1)
obj.add_item(2)
obj.add_item(3)
obj.add_item(4)

f = open(‘custom_class.pkl‘,‘w‘)
pickle.dump(obj, f)
f.close()

# coding=utf-8
import pickle
#import custom_class

f = open(‘custom_class.pkl‘,‘r‘)
obj = pickle.load(f)
f.close()
print obj