[Python常用库]pickle

pickle是Python库中常用的序列化工具，新版本的Python中用c重新实现了一遍，叫cPickle，性能更高，下面的代码演示了pickle库的常用接口用法，非常简单：

import cPickle as pickle

# dumps and loads
# 将内存对象dump为字符串，或者将字符串load为内存对象
def test_dumps_and_loads():
    t = {'name': ['v1', 'v2']}
    print t

    o = pickle.dumps(t)
    print o
    print 'len o: ', len(o)

    p = pickle.loads(o)
    print p


# 关于HIGHEST_PROTOCOL参数，pickle 支持3种protocol，0、1、2：
# http://stackoverflow.com/questions/23582489/python-pickle-protocol-choice
# 0：ASCII protocol，兼容旧版本的Python
# 1：binary format，兼容旧版本的Python
# 2：binary format，Python2.3 之后才有，更好的支持new-sytle class
def test_dumps_and_loads_HIGHEST_PROTOCOL():
    print 'HIGHEST_PROTOCOL: ', pickle.HIGHEST_PROTOCOL

    t = {'name': ['v1', 'v2']}
    print t

    o = pickle.dumps(t, pickle.HIGHEST_PROTOCOL)
    print 'len o: ', len(o)

    p = pickle.loads(o)
    print p


# new-style class
def test_new_sytle_class():
    class TT(object):
        def __init__(self, arg, **kwargs):
            super(TT, self).__init__()
            self.arg = arg
            self.kwargs = kwargs

        def test(self):
            print self.arg
            print self.kwargs

    # ASCII protocol
    t = TT('test', a=1, b=2)
    o1 = pickle.dumps(t)
    print o1
    print 'o1 len: ', len(o1)
    p = pickle.loads(o1)
    p.test()

    # HIGHEST_PROTOCOL对new-style class支持更好，性能更高
    o2 = pickle.dumps(t, pickle.HIGHEST_PROTOCOL)
    print 'o2 len: ', len(o2)
    p = pickle.loads(o2)
    p.test()


# dump and load
# 将内存对象序列化后直接dump到文件或支持文件接口的对象中
# 对于dump，需要支持write接口，接受一个字符串作为输入参数，比如：StringIO
# 对于load，需要支持read接口，接受int输入参数，同时支持readline接口，无输入参数，比如StringIO

# 使用文件，ASCII编码
def test_dump_and_load_with_file():
    t = {'name': ['v1', 'v2']}

    # ASCII format
    with open('test.txt', 'w') as fp:
        pickle.dump(t, fp)

    with open('test.txt', 'r') as fp:
        p = pickle.load(fp)
        print p


# 使用文件，二进制编码
def test_dump_and_load_with_file_HIGHEST_PROTOCOL():
    t = {'name': ['v1', 'v2']}
    with open('test.bin', 'wb') as fp:
        pickle.dump(t, fp, pickle.HIGHEST_PROTOCOL)

    with open('test.bin', 'rb') as fp:
        p = pickle.load(fp)
        print p


# 使用StringIO，二进制编码
def test_dump_and_load_with_StringIO():
    import StringIO

    t = {'name': ['v1', 'v2']}

    fp = StringIO.StringIO()
    pickle.dump(t, fp, pickle.HIGHEST_PROTOCOL)

    fp.seek(0)
    p = pickle.load(fp)
    print p

    fp.close()


# 使用自定义类
# 这里演示用户自定义类，只要实现了write、read、readline接口，
# 就可以用作dump、load的file参数
def test_dump_and_load_with_user_def_class():
    import StringIO

    class FF(object):
        def __init__(self):
            self.buf = StringIO.StringIO()

        def write(self, s):
            self.buf.write(s)
            print 'len: ', len(s)

        def read(self, n):
            return self.buf.read(n)

        def readline(self):
            return self.buf.readline()

        def seek(self, pos, mod=0):
            return self.buf.seek(pos, mod)

        def close(self):
            self.buf.close()

    fp = FF()
    t = {'name': ['v1', 'v2']}
    pickle.dump(t, fp, pickle.HIGHEST_PROTOCOL)

    fp.seek(0)
    p = pickle.load(fp)
    print p

    fp.close()


# Pickler/Unpickler
# Pickler(file, protocol).dump(obj) 等价于 pickle.dump(obj, file[, protocol])
# Unpickler(file).load() 等价于 pickle.load(file)
# Pickler/Unpickler 封装性更好，可以很方便的替换file
def test_pickler_unpickler():
    t = {'name': ['v1', 'v2']}

    f = file('test.bin', 'wb')
    pick = pickle.Pickler(f, pickle.HIGHEST_PROTOCOL)
    pick.dump(t)
    f.close()

    f = file('test.bin', 'rb')
    unpick = pickle.Unpickler(f)
    p = unpick.load()
    print p
    f.close()

原文地址：http://www.isware.cn/python-modules/01-data-persistence-and-exchange/pickle/