簡介

官方API
這個模組主要是做資料序列化和序列化資料解析的，pickle是python語言的庫，cPickle是C語言寫的，後者的執行速度是前者的1000倍。但是cPickle對少數模組不支援。
使用這兩個庫的資料必須是python相關的，否則其他非python語言可能無法解析這些序列化資料。

主要介面

pickle.dump(obj, file[, protocol])
#Write a pickled representation of obj to the open file object file.
#protocol 這裡預設是0, 儲存的檔案在一些編輯器會顯示奇怪，用2可以解決這個問題，下同。
 

pickle.load(file)
#Read a string from the open file object file and interpret it as a pickle data stream, reconstructing and returning the original object hierarchy.
pickle.dumps(obj[, protocol])
#Return the pickled representation of the object as a string, instead of writing it to a file.
pickle.loads(string)
#Read a pickled object hierarchy from a string. 
 

API使用舉例

import pickle
# import cPickle as ...
pickle.dump("123", open("test.txt","wb")) #pickle into file
str1 = pickle.load(open("test.txt","rb")) #load from pickled file

當然在dump或者load過程中遇到錯誤會有異常丟擲，可以檢視上面的API獲取異常的型別。

操作複雜物件

pickle操作複雜資料結構或者物件、函式等：

#!/usr/bin/env python
#-*- coding:utf-8 -*-
 

############################
#File Name: pickle_test.py
#Author: Wang 
#Mail: [email protected]
#Created Time:2017-09-23 16:56:53
############################

from pickle import *

my_dict = {'name':'wang', 'age':15}
print "initial dict: ", my_dict
ss = dumps(my_dict)
tt = loads(ss)
print "loaded dict: ", tt

def my_func(x, y):
    print "the number inputted: %d,%d, sum is: "%(x,y),
    return x + y
ss = dumps(my_func)
tt = loads(ss)
print "loaded function: ", tt(2,4)

import numpy as np
class My_class:
    def __init__(self):
        self.name = "Lee"
    self.sex = "male"
    self.index = np.array([1,2,3])
    def set_name(self, newname):
        self.name = newname
    def get_sub(self, a, b):
        return a - b

my_obj = My_class()
my_obj.set_name("Zhao")
print my_obj
ss = dumps(my_obj)
tt = loads(ss)
print tt
print tt.name, tt.index, tt.get_sub(12,10)
'''
Results:
initial dict:  {'age': 15, 'name': 'wang'}
loaded dict:  {'age': 15, 'name': 'wang'}
loaded function:  the number inputted: 2,4, sum is:  6
<__main__.My_class instance at 0x7f917a3c42d8>
<__main__.My_class instance at 0x7f9162d8d290>
Zhao [1 2 3] 2   
'''

從上面結果知，pickle可以處理python的函式、複雜資料和物件，但是物件儲存也是把之前的物件拷貝下來，比如這裡列印結果是Zhao不是初始化的Wang。

和ROS結合

這裡dumps()將資料壓縮成字串格式，在rospy裡面可以把這種String訊息型別發出去，從而實現在ros裡複雜結構、函式和物件的釋出。舉例：

#!/usr/bin/env python
# license removed for brevity
import rospy
from std_msgs.msg import String
from pickle import *

import numpy as np
class My_class:
    def __init__(self):
        self.name = "Lee"
    self.sex = "male"
    self.index = np.array([1,2,3])
    def set_name(self, newname):
        self.name = newname
    def get_sub(self, a, b):
        return a - b

def talker():
    pub = rospy.Publisher('chatter', String, queue_size=10)
    rospy.init_node('talker', anonymous=True)
    rate = rospy.Rate(10) # 10hz
    while not rospy.is_shutdown():
        hello_str = dumps(My_class)
        rospy.loginfo(hello_str)
        pub.publish(hello_str)
        rate.sleep()

if __name__ == '__main__':
    try:
        talker()
    except rospy.ROSInterruptException:
        pass