Python 与 Pickle

用于序列化的两个模块
　　json：用于字符串和Python数据类型间进行转换
　　pickle: 用于python特有的类型和python的数据类型间进行转换
　　json提供四个功能：dumps,dump,loads,load
　　pickle提供四个功能：dumps,dump,loads,load

pickle可以存储什么类型的数据呢？

1. 所有python支持的原生类型：布尔值，整数，浮点数，复数，字符串，字节，None。
2. 由任何原生类型组成的列表，元组，字典和集合。
3. 函数，类，类的实例

pickle模块中常用的方法有：

    1. pickle.dump(obj, file, protocol=None,)

    必填参数obj表示将要封装的对象

    必填参数file表示obj要写入的文件对象，file必须以二进制可写模式打开，即“wb”

    可选参数protocol表示告知pickler使用的协议，支持的协议有0,1,2,3，默认的协议是添加在Python 3中的协议3。　　　

• Protocol version 0 is the original “human-readable” protocol and is backwards compatible with earlier versions of Python.
• Protocol version 1 is an old binary format which is also compatible with earlier versions of Python.
• Protocol version 2 was introduced in Python 2.3. It provides much more efficient pickling of new-style classes. Refer to PEP 307 for information about improvements brought by protocol 2.
• Protocol version 3 was added in Python 3.0. It has explicit support for bytes objects and cannot be unpickled by Python 2.x. This is the default protocol, and the recommended protocol when compatibility with other Python 3 versions is required.
• Protocol version 4 was added in Python 3.4. It adds support for very large objects, pickling more kinds of objects, and some data format optimizations. Refer to PEP 3154 for information about improvements brought by protocol 4. 

    2. pickle.load(file,*,fix_imports=True, encoding="ASCII", errors="strict")

    必填参数file必须以二进制可读模式打开，即“rb”，其他都为可选参数

    3. pickle.dumps(obj)：以字节对象形式返回封装的对象，不需要写入文件中

    4. pickle.loads(bytes_object): 从字节对象中读取被封装的对象，并返回

 pickle模块可能出现三种异常：

    1. PickleError：封装和拆封时出现的异常类，继承自Exception

    2. PicklingError: 遇到不可封装的对象时出现的异常，继承自PickleError

    3. UnPicklingError: 拆封对象过程中出现的异常，继承自PickleError

import pickle

# 对于pickle内部的数据是二进制式的字符串 （bytes）
# dumps 功能 python ====> pickle bytes
data = ['aa', 'bb', 'cc']
p_str = pickle.dumps(data)
print(p_str)
print(type(p_str))

# loads 功能，pickle bytes ====> python 的数据结构
data1 = pickle.loads(p_str)
print(data1)
print(type(data1))
print("中国: ", bytes("中国", encoding='utf-8'))

# dump 功能
# dump 将数据通过特殊的形式转化为只有python语言认识的字符串，并写入文件
# dump,load 对文件操作，必须是二进制的方式，wb，rb
with open("tmp.pk", 'wb') as f:
    pickle.dump(data, f)

# load 功能
# pickle 文件 =====> python数据结构

with open("tmp.pk", 'rb') as f:
    data_from_picklefile = pickle.load(f)
print(data_from_picklefile)