pickle/cPickle操作函数、对象及在ROS中发布复杂消息

简介

官方API
这个模块主要是做数据串行化和串行化数据解析的，pickle是python语言的库，cPickle是C语言写的，后者的执行速度是前者的1000倍。但是cPickle对少数模块不支持。
使用这两个库的数据必须是python相关的，否则其他非python语言可能无法解析这些串行化数据。

主要接口

pickle.dump(obj, file[, protocol])#Write a pickled representation of obj to the open file object file.#protocol 这里默认是0, 保存的文件在一些编辑器会显示奇怪，用2可以解决这个问题，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使用举例

import pickle# import cPickle as ...pickle.dump("123", open("test.txt","wb")) #pickle into filestr1 = pickle.load(open("test.txt","rb")) #load from pickled file

当然在dump或者load过程中遇到错误会有异常抛出，可以查看上面的API获取异常的类型。

操作复杂对象

pickle操作复杂数据结构或者对象、函数等：

#!/usr/bin/env python#-*- coding:utf-8 -*-#############################File Name: pickle_test.py#Author: Wang #Mail: [e-mail]#Created Time:2017-09-23 16:56:53############################from pickle import *my_dict = {'name':'wang', 'age':15}print "initial dict: ", my_dictss = dumps(my_dict)tt = loads(ss)print "loaded dict: ", ttdef my_func(x, y):    print "the number inputted: %d,%d, sum is: "%(x,y),    return x + yss = dumps(my_func)tt = loads(ss)print "loaded function: ", tt(2,4)import numpy as npclass 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 - bmy_obj = My_class()my_obj.set_name("Zhao")print my_objss = dumps(my_obj)tt = loads(ss)print ttprint 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   '''

从上面结果知，pickle可以处理python的函数、复杂数据和对象，但是对象存储也是把之前的对象拷贝下来，比如这里打印结果是Zhao不是初始化的Wang。

和ROS结合

这里dumps()将数据压缩成字符串格式，在rospy里面可以把这种String消息类型发出去，从而实现在ros里复杂结构、函数和对象的发布。举例：

#!/usr/bin/env python# license removed for brevityimport rospyfrom std_msgs.msg import Stringfrom pickle import *import numpy as npclass 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 - bdef 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