Python解析xml文件： ElementTree解析xml换行和缩进美化问题

问题摘要

在使用python中的xml.etree.ElementTree库解析xml文件时，默认不会做任何的换行和缩进处理，导致输出的xml文件阅读起来很不方便。以高通平台小基站射频校准配置文件为例，笔者希望该xml文件的格式如下所示，这样很容易找出Tx、Rx、Nl等等射频链路的校准配置。

<CalConfigDefinitions>
	<BoardConfigs>
		<BoardDef name="F02001-2" configs="F02001-2_LTE20" />
	BoardConfigs>
	<CalConfigs>
		<CalConfig name="F02001-2_LTE5" topology="407">
			<TxConfig txPathIdList="TX1,TX2" antennaNum="1,2" bwConst="LTE5" band="B41" fg="2" enableFb="false" txRefFreq="2590" listOfTxSweepFreqMhz="2498.5,2510.5,2520.5,2530.5,2540.5,2560.5,2580.5,2600.5,2620.5,2640.5,2660.5,2670.5,2680.5,2687.5" firstGainState="40" firstGainStatePowerLimitHigh="10" firstGainStatePowerLimitLow="-45" highestAllowedGainState="0" targetMaxPower="17" txDcLeakageLimit="-40" txIqImageLimit="-40" maxFreqSweepPeakToPeakDelta="10" rxFbDcLeakageLimitDbfs="-34" rxFbIqImageLimitDbc="-40" rxfbSignalDbfsMin="-20" rxfbSignalDbfsMax="0" txFreqSweepTargetReferencePowerDbm="17" txDigitalGainMaxDb="-3" txHighDcLeakageLimit="-43" txLowCutoffGainState="30" calDataAlsoAppliesTo="LTE10,LTE15,LTE20" txMonotonicCheckThresholdDb="-3" />
			<RxFb1AclrNoiseCal rxfbPathIdList="FB1,FB2" bwConst="LTE5" band="B41" fg="2" freq="2590" rxfbMaxGainState="16" />
			<RxConfig rxPathIdList="RX1,RX2" antennaNum="1,2" bwConst="LTE5" band="B41" fg="2" rxRefFreqMhz="2590" listOfRxSweepFreqMhz="2498.5,2510.5,2520.5,2530.5,2540.5,2560.5,2580.5,2600.5,2620.5,2640.5,2660.5,2670.5,2680.5,2687.5" rxGainStateList="0,1,2,3,4,5,6,7" rxSigGenPowersForGainState="-66,-59,-56,-51,-46,-41,-31,-21" rxDcLeakageLimitDbfs="-40" rxIqImageLimitDbc="-40" maxFreqSweepPeakToPeakDelta="10" rxSignalDbfsMin="-40" rxSignalDbfsMax="-20" calDataAlsoAppliesTo="LTE10,LTE15,LTE20" />
			<RxConfig rxPathIdList="NL1" antennaNum="3" bwConst="LTE20" band="B25" fg="3" rxRefFreqMhz="1960" listOfRxSweepFreqMhz="1930,1940,1945,1950,1955,1960,1965,1970,1975,1980,1985,1990,1995" rxGainStateList="0,1,2,3,4,5" rxSigGenPowersForGainState="-65,-57,-51,-40,-29,-18" rxDcLeakageLimitDbfs="-40" rxIqImageLimitDbc="-40" maxFreqSweepPeakToPeakDelta="10" rxSignalDbfsMin="-40" rxSignalDbfsMax="-20" />
		CalConfig>
	CalConfigs>
CalConfigDefinitions>

而实际Python xml.etree.ElementTree库默认输出的xml文件如下，所有节点堆积在同一行。下面通过增加换行和缩进来美化xml文件，读者不需要纠结该xml文件的实际意义，本文仅以此为例。

<CalConfigDefinitions><BoardConfigs><BoardDef name="F02001-2" configs="F02001-2_LTE20" />BoardConfigs><CalConfigs><CalConfig name="F02001-2_LTE5" topology="407"><TxConfig txPathIdList="TX1,TX2" antennaNum="1,2" bwConst="LTE5" band="B41" fg="2" enableFb="false" txRefFreq="2590" listOfTxSweepFreqMhz="2498.5,2510.5,2520.5,2530.5,2540.5,2560.5,2580.5,2600.5,2620.5,2640.5,2660.5,2670.5,2680.5,2687.5" firstGainState="40" firstGainStatePowerLimitHigh="10" firstGainStatePowerLimitLow="-45" highestAllowedGainState="0" targetMaxPower="17" txDcLeakageLimit="-40" txIqImageLimit="-40" maxFreqSweepPeakToPeakDelta="10" rxFbDcLeakageLimitDbfs="-34" rxFbIqImageLimitDbc="-40" rxfbSignalDbfsMin="-20" rxfbSignalDbfsMax="0" txFreqSweepTargetReferencePowerDbm="17" txDigitalGainMaxDb="-3" txHighDcLeakageLimit="-43" txLowCutoffGainState="30" calDataAlsoAppliesTo="LTE10,LTE15,LTE20" txMonotonicCheckThresholdDb="-3" /><RxFb1AclrNoiseCal rxfbPathIdList="FB1,FB2" bwConst="LTE5" band="B41" fg="2" freq="2590" rxfbMaxGainState="16" /><RxConfig rxPathIdList="RX1,RX2" antennaNum="1,2" bwConst="LTE5" band="B41" fg="2" rxRefFreqMhz="2590" listOfRxSweepFreqMhz="2498.5,2510.5,2520.5,2530.5,2540.5,2560.5,2580.5,2600.5,2620.5,2640.5,2660.5,2670.5,2680.5,2687.5" rxGainStateList="0,1,2,3,4,5,6,7" rxSigGenPowersForGainState="-66,-59,-56,-51,-46,-41,-31,-21" rxDcLeakageLimitDbfs="-40" rxIqImageLimitDbc="-40" maxFreqSweepPeakToPeakDelta="10" rxSignalDbfsMin="-40" rxSignalDbfsMax="-20" calDataAlsoAppliesTo="LTE10,LTE15,LTE20" /><RxConfig rxPathIdList="NL1" antennaNum="3" bwConst="LTE20" band="B25" fg="3" rxRefFreqMhz="1960" listOfRxSweepFreqMhz="1930,1940,1945,1950,1955,1960,1965,1970,1975,1980,1985,1990,1995" rxGainStateList="0,1,2,3,4,5" rxSigGenPowersForGainState="-65,-57,-51,-40,-29,-18" rxDcLeakageLimitDbfs="-40" rxIqImageLimitDbc="-40" maxFreqSweepPeakToPeakDelta="10" rxSignalDbfsMin="-40" rxSignalDbfsMax="-20" />CalConfig>CalConfigs>CalConfigDefinitions>

软件环境说明

Python版本： Python 3.7
Xml解析库： xml.etree.ElementTree
IDE： PyCharm

网络上xml美化方法

遇到问题首先想到的是搜一下大神们是如何操作的，网上的解决办法基本上大同小异：在创建好所有节点之后、初始化tree之前进行换行(\n)和缩进(\t)处理，如以下部分代码所示。

def prettyXml(self,tree,indent,newline,level=0):
    """
    Pretty Xml File before writing
    :param tree: 创建好的父节点，未初始化的tree
    :param indent: 缩进“\t”
    :param newline: 换行“\n”
    :param level: 用于递归操作的变量，实现不同级别节点增加不同数量的缩进“\t”
    :return: 无
    """
    treeList=list(tree)
    for subElement in treeList:
        # print(subElement)
        if treeList.index(subElement) < (len(treeList) - 1):
            subElement.tail=newline+indent*(level+1)
        else:
            subElement.tail=newline+indent*level
        self.prettyXml(subElement,indent,newline,level+1)

# parent_node的创建过程省略
prettyXml(parent_node,'\t','\n')		# 换行和缩进处理
tree=ET.ElementTree(parent_node)		# 初始化tree，ET为导入的xml.etree.ElementTree，导入过程省略
write_xml(tree, r"E:\2_PersonalStudy\1_PythonStudy\MyPyCharmProject\TestDemo\venv\Output\Test.xml") 	# 生成xml文件，方法省略

通过以上处理后，可以得到如下xml文件。看起来要美观很多，但是和笔者想要得到的结果还有一定差距。返回来查看上述prettyXml方法，只能实现在节点的tail处增加换行和缩进处理，对于父节点CalConfigDefinitions、BoardConfigs、CalConfigs的“<…>”末尾处无法处理，这是该方法的不足之处，需要进一步处理。

<CalConfigDefinitions><BoardConfigs><BoardDef name="F02001-2" configs="F02001-2_LTE20" />
	BoardConfigs>
	<CalConfigs><CalConfig name="F02001-2_LTE5" topology="407"><TxConfig txPathIdList="TX1,TX2" antennaNum="1,2" bwConst="LTE5" band="B41" fg="2" enableFb="false" txRefFreq="2590" listOfTxSweepFreqMhz="2498.5,2510.5,2520.5,2530.5,2540.5,2560.5,2580.5,2600.5,2620.5,2640.5,2660.5,2670.5,2680.5,2687.5" firstGainState="40" firstGainStatePowerLimitHigh="10" firstGainStatePowerLimitLow="-45" highestAllowedGainState="0" targetMaxPower="17" txDcLeakageLimit="-40" txIqImageLimit="-40" maxFreqSweepPeakToPeakDelta="10" rxFbDcLeakageLimitDbfs="-34" rxFbIqImageLimitDbc="-40" rxfbSignalDbfsMin="-20" rxfbSignalDbfsMax="0" txFreqSweepTargetReferencePowerDbm="17" txDigitalGainMaxDb="-3" txHighDcLeakageLimit="-43" txLowCutoffGainState="30" calDataAlsoAppliesTo="LTE10,LTE15,LTE20" txMonotonicCheckThresholdDb="-3" />
			<RxFb1AclrNoiseCal rxfbPathIdList="FB1,FB2" bwConst="LTE5" band="B41" fg="2" freq="2590" rxfbMaxGainState="16" />
			<RxConfig rxPathIdList="RX1,RX2" antennaNum="1,2" bwConst="LTE5" band="B41" fg="2" rxRefFreqMhz="2590" listOfRxSweepFreqMhz="2498.5,2510.5,2520.5,2530.5,2540.5,2560.5,2580.5,2600.5,2620.5,2640.5,2660.5,2670.5,2680.5,2687.5" rxGainStateList="0,1,2,3,4,5,6,7" rxSigGenPowersForGainState="-66,-59,-56,-51,-46,-41,-31,-21" rxDcLeakageLimitDbfs="-40" rxIqImageLimitDbc="-40" maxFreqSweepPeakToPeakDelta="10" rxSignalDbfsMin="-40" rxSignalDbfsMax="-20" calDataAlsoAppliesTo="LTE10,LTE15,LTE20" />
			<RxConfig rxPathIdList="NL1" antennaNum="3" bwConst="LTE20" band="B25" fg="3" rxRefFreqMhz="1960" listOfRxSweepFreqMhz="1930,1940,1945,1950,1955,1960,1965,1970,1975,1980,1985,1990,1995" rxGainStateList="0,1,2,3,4,5" rxSigGenPowersForGainState="-65,-57,-51,-40,-29,-18" rxDcLeakageLimitDbfs="-40" rxIqImageLimitDbc="-40" maxFreqSweepPeakToPeakDelta="10" rxSignalDbfsMin="-40" rxSignalDbfsMax="-20" />
		CalConfig>
	CalConfigs>
CalConfigDefinitions>

网络上xml美化方法进一步优化

让我们站在大神们的肩膀上继续成长。既然prettyXml方法只能在tail处操作，那是否可以通过修改ElementTree.py源码实现"<…>"末尾处换行和缩进呢？

查找ElementTree.py源码，发现可以在 _serialize_xml方法中增加换行和缩进处理，修改后的代码如下（代码中还去除了节点属性的默认排序功能，读者可忽略此部分处理，如果感兴趣可以查看笔者的另一篇关于xml节点属性排序问题的博客）。

综上，通过修改_serialize_xml方法并结合使用prettyXml方法，便可以输出问题摘要章节中笔者想要得到的xml文件。

def _serialize_xml(write, elem, qnames, namespaces,
                   short_empty_elements, level=1, **kwargs):		# 增加level参数，用于递归操作，不同级别节点增加不同数量的“\t”
    tag = elem.tag
    text = elem.text
    if tag is Comment:
        write("" % text)
    elif tag is ProcessingInstruction:
        write("" % text)
    else:
        tag = qnames[tag]
        if tag is None:
            if text:
                write(_escape_cdata(text))
            for e in elem:
                _serialize_xml(write, e, qnames, None,
                               short_empty_elements=short_empty_elements)
        else:
            write("<" + tag)
            items = list(elem.items())
            if items or namespaces:
                if namespaces:
                    for v, k in sorted(namespaces.items(),
                                       key=lambda x: x[1]):  
                        if k:
                            k = ":" + k
                        write(" xmlns%s=\"%s\"" % (
                            k,
                            _escape_attrib(v)
                            ))
                for k, v in items: 		# 【此处可不做关注】和源码比较，去掉了sorted方法，实现节点属性顺序的自定义
                    if isinstance(k, QName):
                        k = k.text
                    if isinstance(v, QName):
                        v = qnames[v.text]
                    else:
                        v = _escape_attrib(v)
                    write(" %s=\"%s\"" % (qnames[k], v))
            if text or len(elem) or not short_empty_elements:
                write(">\n" + level * "\t")  							# 在>处增加“\n”和“\t”
                if text:
                    write(_escape_cdata(text))
                for e in elem:
                    _serialize_xml(write, e, qnames, None,
                                   short_empty_elements=short_empty_elements,level=level+1)	# 增加level参数，低级别节点“\t”加1
                write(" + tag + ">")
            else:
                write(" />")
    if elem.tail:
        write(_escape_cdata(elem.tail))

重写ElementTree.py源码思考

虽然已经实现了xml文件的美化，但是我们是通过修改 _serialize_xml和使用prettyXml来实现的，其实完全可以合并到一起，也就是将节点tail的处理也加入到_serialize_xml方法中，代码如下，输出xml的效果是一样的。

def _serialize_xml(write, elem, qnames, namespaces,
                   short_empty_elements, level=1, **kwargs):		# 增加level参数，用于递归操作，不同级别节点增加不同数量的“\t”
    tag = elem.tag
    text = elem.text
    if tag is Comment:
        write("" % text)
    elif tag is ProcessingInstruction:
        write("" % text)
    else:
        tag = qnames[tag]
        if tag is None:
            if text:
                write(_escape_cdata(text))
            for e in elem:
                _serialize_xml(write, e, qnames, None,
                               short_empty_elements=short_empty_elements)
        else:
            write("<" + tag)
            items = list(elem.items())
            if items or namespaces:
                if namespaces:
                    for v, k in sorted(namespaces.items(),
                                       key=lambda x: x[1]):  # sort on prefix
                        if k:
                            k = ":" + k
                        write(" xmlns%s=\"%s\"" % (
                            k,
                            _escape_attrib(v)
                            ))
                for k, v in items:  # 【此处可不做关注】和源码比较，去掉了sorted方法，实现节点属性顺序的自定义
                    if isinstance(k, QName):
                        k = k.text
                    if isinstance(v, QName):
                        v = qnames[v.text]
                    else:
                        v = _escape_attrib(v)
                    write(" %s=\"%s\"" % (qnames[k], v))
            if text or len(elem) or not short_empty_elements:
                write(">\n" + level * "\t")		# 在>处增加“\n”和“\t”
                if text:
                    write(_escape_cdata(text))
                elemList=list(elem)			# 将elem转化成列表
                for e in elem:				# 循环处理各个节点
                    if elemList.index(e) < (len(elemList) - 1):
                        e.tail = "\n" + "\t" * (level)		# 父节点的子节点换行和缩进处理（最后一个子节点除外）
                    else:
                        e.tail = "\n" + "\t" * (level - 1)	# 父节点的最后一个子节点换行和缩进处理
                    _serialize_xml(write, e, qnames, None,
                                   short_empty_elements=short_empty_elements,level=level+1)	# 增加level参数，低级别节点“\t”加1
                write(" + tag + ">")
            else:
                write(" />")
    if elem.tail:
        write(_escape_cdata(elem.tail))

总结说明

1. 代码的优化永无止境，小白一枚，欢迎大家一起探讨；
2. 此文档仅用于Python学习记录和交流，如能帮助到读者倍感荣幸。