Python dict/list mix不是JSON serializab

Question

我有点困惑。我试图构建JSON字符串，它在我的程序中生成一个回溯。真正奇怪的是，如果我将其剪切并粘贴到一个控制台上，整个过程都会起作用。在

首先，这是密码。在

    def readgs2JSON(self, msg):
    d = {"Channel" : "Readings"}
    d["Sensor"] = msg.ReadingsChn.ReadingReport.attrib["Sensor"]
    d["ReadingID"] = msg.ReadingsChn.ReadingReport.attrib["ReadingID"]
    d["Detect"] = msg.ReadingsChn.ReadingReport.Data.attrib["Detect"]
    d["Level"] = msg.ReadingsChn.ReadingReport.Data.attrib["Level"]
    d["Units"] = msg.ReadingsChn.ReadingReport.Data.attrib["Units"]
    if "Id" in msg.ReadingsChn.ReadingReport.Data.attrib:
        d["Id"] = msg.ReadingsChn.ReadingReport.Data.attrib["Id"]
    d["SUD"] = [el.attrib for el in msg.ReadingsChn.ReadingReport.Data.iterchildren()]
    print d
    return d

变量msg是lxml生成的一个对象化元素。由代码生成的dictionary，d在打印时是这样的。（抱歉，这很难读懂。它似乎不想很好地换行。）

^{pr2}$

所以，当我执行json.dumps文件（d） 在我的程序中，我得到了回溯：

[Failure instance: Traceback: <type 'exceptions.TypeError'>: {'Type':   'int', 'Name': 'Reading1', 'Value': '75856'} is not JSON serializable
/usr/lib64/python2.7/site-packages/twisted/internet/base.py:1195:run
/usr/lib64/python2.7/site-packages/twisted/internet/base.py:1204:mainLoop
/usr/lib64/python2.7/site-packages/twisted/internet 
/base.py:825:runUntilCurrent
/usr/lib64/python2.7/site-packages/twisted/internet/task.py:239:__call__
--- <exception caught here> ---
/usr/lib64/python2.7/site-packages/twisted/internet
/defer.py:149:maybeDeferred
/home/max/workspace/canary/CCSIEventHandler.py:26:tick
/home/max/workspace/canary/CCSIEventHandler.py:99:event2Msg
/home/max/workspace/canary/sensorcache.py:715:writeToBuffer
/home/max/workspace/canary/CCSI2JSON.py:37:pushCCSIMessage
/usr/lib64/python2.7/json/__init__.py:244:dumps
/usr/lib64/python2.7/json/encoder.py:207:encode
/usr/lib64/python2.7/json/encoder.py:270:iterencode
/usr/lib64/python2.7/json/encoder.py:184:default
]

所以，真正奇怪的是，如果我从终端复制打印出来的dict，并将其传递到python控制台中，那么整个过程都会成功！在

>>> json.dumps(d)
'{"SUD": [{"Type": "int", "Name": "Reading1", "Value": "75856"}, {"Type": "int", "Name": "Reading2", "Value": "75857"}, {"Type": "int", "Name": "Reading3", "Value": "75858"}, {"Type": "int", "Name": "Reading4", "Value": "75859"}, {"Type": "int", "Name": "ClockTicks", "Value": "389"}, {"Type": "array", "Name": "Spectrum", "Value": "None"}], "Level": "0", "Detect": "NONE", "Units": "bars", "ReadingID": "R000009233", "Sensor": "SC001", "Channel": "Readings"}'

在我的一生中，我无法发现区别，但我不是JSON专家。其他人有这个问题吗？在

结果我想把lxml.etree这是一个字典，我认为它是一个字典，因为它像一个dict一样工作。这是一个调整后的代码，可以构建一个字典，并且可以正常工作。在

    def readgs2JSON(self, msg):
    d = {"Channel" : "Readings"}
    d["Sensor"] = msg.ReadingsChn.ReadingReport.attrib["Sensor"]
    d["ReadingID"] = msg.ReadingsChn.ReadingReport.attrib["ReadingID"]
    d["Detect"] = msg.ReadingsChn.ReadingReport.Data.attrib["Detect"]
    d["Level"] = msg.ReadingsChn.ReadingReport.Data.attrib["Level"]
    d["Units"] = msg.ReadingsChn.ReadingReport.Data.attrib["Units"]
    if "Id" in msg.ReadingsChn.ReadingReport.Data.attrib:
        d["Id"] = msg.ReadingsChn.ReadingReport.Data.attrib["Id"]
    sud_list = []
    for el in msg.ReadingsChn.ReadingReport.Data.iterchildren():
        sud_dict = {}
        for item in el.attrib:
            sud_dict[item] = el.attrib[item]
        sud_list.append(sud_dict)
    if sud_list is not []:
        d["SUD"] = sud_list
    return d

Answer 1

msg.ReadingsChn.ReadingReport.Data的子级是某种特殊类型的，它们不能JSON序列化。它被正确打印到控制台的原因是因为该类型重写了__str__或{}。在