PyCon 2011 - Hidden Treasures of the Python Standard Library - json序列化操作

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作者：liuyuan_jq

2011-03-30

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json简介

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JSON(JavaScript Object Notation) 是一种轻量级的数据交换格式。 易于人阅读和编写。同时也易于机器解析和生成。 它基于JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999的一个子集。 JSON采用完全独立于语言的文本格式，但是也使用了类似于C语言家族的习惯（包括C, C++, C#, Java, JavaScript, Perl, Python等）。 这些特性使JSON成为理想的数据交换语言。

json资源

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http://www.json.org/json-zh.html

http://woodpecker.org.cn/diveintopython3/serializing.html

simplejson

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如果你使用的是python2.6以下的版本，需要手动安装simplejson支持json

easy_install simplejson

自定义序列化对象

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#!/usr/bin/env python
# encoding: utf-8
# json_myobj.py
""" Define a class to be encoded.
"""
class MyObj(object):
    def __init__(self, s):
        self.s = s
    def __repr__(self):
        return '<MyObj(%s)>' % self.s

dumps操作

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#!/usr/bin/env python
# encoding: utf-8
# json_dump_default.py
"""Serialize a custom object to JSON.
"""
import hmac
import json_myobj
try:
    import json
except:
    import simplejson as json
"""
# python json_dump_default.py
{
    "s"            : "instance value goes here", 
    "__module__"   : "json_myobj", 
    "__signature__": "426f662f9fe3b3533d9ce7f9dcf8af77", 
    "__class__"    : "MyObj"
}
"""
def convert_to_builtin_type(obj):
    """object->dictionary"""
    print 'convert_to_builtin_type(%r)' % obj
    # convert_to_builtin_type(<MyObj(instance value goes here)>)
    class_name = obj.__class__.__name__
    module_name = obj.__module__
    digest_maker = hmac.new('PyCon2011',              # 公钥
                            module_name + class_name) # 发送的信息
    signature = digest_maker.hexdigest() # 生成摘要
    d = { '__class__':class_name,
          '__module__':module_name,
          '__signature__':signature,
          }
    d.update(obj.__dict__)
    return d
obj = json_myobj.MyObj('instance value goes here')
print json.dumps(obj, default=convert_to_builtin_type)

loads操作

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#!/usr/bin/env python
# encoding: utf-8
"""Load a custom object from JSON serlized version.
"""
import hmac
try:
    import json
except:
    import simplejson as json
def dict_to_object(d):    
    if '__class__' not in d: 
        return d
        
    class_name = d.pop('__class__')
    module_name = d.pop('__module__')
    signature = d.pop('__signature__')
    digest_maker = hmac.new('PyCon2011', 
                            module_name + class_name)
    expected_signature = digest_maker.hexdigest()
    if signature != expected_signature:
        raise ValueError('Invalid signature')
    
    print 'Loading "%s" from "%s"' % \
        (class_name, module_name)
    module = __import__(module_name)
    class_ = getattr(module, class_name)
    
    args = dict( (key.encode('ascii'), value)
                 for key, value in d.items())
    print 'Instantiating with', args
    
    inst = class_(**args)
    return inst
for encoded_object in [
    '''
    [{"s": "instance value goes here",
      "__signature__": "426f662f9fe3b3533d9ce7f9dcf8af77",
      "__module__": "json_myobj", "__class__": "MyObj"}]
    ''',
    
    # careful!
    '''
    [{"path": "/etc/passwd",
      "__signature__": "426f662f9fe3b3533d9ce7f9dcf8af77",
      "__module__": "os", "__class__": "unlink"}]
    ''',
    ]:
    try:
        myobj_instance = json.loads(
            encoded_object, 
            object_hook=dict_to_object,
            )
        print myobj_instance
    except Exception, err:
        print 'ERROR:', err
    print