用Python解析XML的几种常见方法的介绍
一、简介
XML（eXtensible Markup Language）指可扩展标记语言，被设计用来传输和存储数据，已经日趋成为当前许多新生技术的核心，在不同的领域都有着不同的应用。它是web发展到一定阶段的必然产物，既具有SGML的核心特征，又有着HTML的简单特性，还具有明确和结构良好等许多新的特性。
python解析XML常见的有三种方法：一是xml.dom.*模块，它是W3C DOM API的实现，若需要处理DOM API则该模块很适合，注意xml.dom包里面有许多模块，须区分它们间的不同；二是xml.sax.*模块，它是SAX API的实现，这个模块牺牲了便捷性来换取速度和内存占用，SAX是一个基于事件的API，这就意味着它可以“在空中”处理庞大数量的的文档，不用完全加载进内存；三是xml.etree.ElementTree模块（简称 ET），它提供了轻量级的Python式的API，相对于DOM来说ET 快了很多，而且有很多令人愉悦的API可以使用，相对于SAX来说ET的ET.iterparse也提供了 “在空中” 的处理方式，没有必要加载整个文档到内存，ET的性能的平均值和SAX差不多，但是API的效率更高一点而且使用起来很方便。
二、详解
解析的xml文件（country.xml）：
在CODE上查看代码片派生到我的代码片
<?xml version="1.0"?>
<data>
<country name="Singapore">
<rank>4</rank>
<year>2011</year>
<gdppc>59900</gdppc>
<neighbor name="Malaysia" direction="N"/>
</country>
<country name="Panama">
<rank>68</rank>
<year>2011</year>
<gdppc>13600</gdppc>
<neighbor name="Costa Rica" direction="W"/>
<neighbor name="Colombia" direction="E"/>
</country>
</data>
1、xml.etree.ElementTree
ElementTree生来就是为了处理XML，它在Python标准库中有两种实现：一种是纯Python实现的，如xml.etree.ElementTree，另一种是速度快一点的xml.etree.cElementTree。注意：尽量使用C语言实现的那种，因为它速度更快，而且消耗的内存更少。
在CODE上查看代码片派生到我的代码片
try:
import xml.etree.cElementTree as ET
except ImportError:
import xml.etree.ElementTree as ET
这是一个让Python不同的库使用相同API的一个比较常用的办法，而从Python 3.3开始ElementTree模块会自动寻找可用的C库来加快速度，所以只需要import xml.etree.ElementTree就可以了。
在CODE上查看代码片派生到我的代码片
#!/usr/bin/evn python
#coding:utf-8
try:
import xml.etree.cElementTree as ET
except ImportError:
import xml.etree.ElementTree as ET
import sys
try:
tree = ET.parse("country.xml") #打开xml文档
#root = ET.fromstring(country_string) #从字符串传递xml
root = tree.getroot() #获得root节点
except Exception, e:
print "Error:cannot parse file:country.xml."
sys.exit(1)
print root.tag, "---", root.attrib
for child in root:
print child.tag, "---", child.attrib
print "*"*10
print root[0][1].text #通过下标访问
print root[0].tag, root[0].text
print "*"*10
for country in root.findall('country'): #找到root节点下的所有country节点
rank = country.find('rank').text #子节点下节点rank的值
name = country.get('name') #子节点下属性name的值
print name, rank
#修改xml文件
for country in root.findall('country'):
rank = int(country.find('rank').text)
if rank > 50:
root.remove(country)
tree.write('output.xml')
运行结果：
参考：https://docs.python.org/2/library/xml.etree.elementtree.html
2、xml.dom.*
文件对象模型（Document Object Model，简称DOM），是W3C组织推荐的处理可扩展置标语言的标准编程接口。一个 DOM 的解析器在解析一个XML文档时，一次性读取整个文档，把文档中所有元素保存在内存中的一个树结构里，之后你可以利用DOM 提供的不同的函数来读取或修改文档的内容和结构，也可以把修改过的内容写入xml文件。python中用xml.dom.minidom来解析xml文件，例子如下：
在CODE上查看代码片派生到我的代码片
#!/usr/bin/python
#coding=utf-8
from xml.dom.minidom import parse
import xml.dom.minidom
# 使用minidom解析器打开XML文档
DOMTree = xml.dom.minidom.parse("country.xml")
Data = DOMTree.documentElement
if Data.hasAttribute("name"):
print "name element : %s" % Data.getAttribute("name")
# 在集合中获取所有国家
Countrys = Data.getElementsByTagName("country")
# 打印每个国家的详细信息
for Country in Countrys:
print "*****Country*****"
if Country.hasAttribute("name"):
print "name: %s" % Country.getAttribute("name")
rank = Country.getElementsByTagName('rank')[0]
print "rank: %s" % rank.childNodes[0].data
year = Country.getElementsByTagName('year')[0]
print "year: %s" % year.childNodes[0].data
gdppc = Country.getElementsByTagName('gdppc')[0]
print "gdppc: %s" % gdppc.childNodes[0].data
for neighbor in Country.getElementsByTagName("neighbor"):
print neighbor.tagName, ":", neighbor.getAttribute("name"), neighbor.getAttribute("direction")
运行结果：
参考：https://docs.python.org/2/library/xml.dom.html
3、xml.sax.*
SAX是一种基于事件驱动的API，利用SAX解析XML牵涉到两个部分：解析器和事件处理器。其中解析器负责读取XML文档，并向事件处理器发送事件，如元素开始跟元素结束事件；而事件处理器则负责对事件作出相应，对传递的XML数据进行处理。python中使用sax方式处理xml要先引入xml.sax中的parse函数，还有xml.sax.handler中的ContentHandler。常使用在如下的情况下：一、对大型文件进行处理；二、只需要文件的部分内容，或者只需从文件中得到特定信息；三、想建立自己的对象模型的时候。
ContentHandler类方法介绍
（1）characters(content)方法
调用时机：
从行开始，遇到标签之前，存在字符，content的值为这些字符串。
从一个标签，遇到下一个标签之前， 存在字符，content的值为这些字符串。
从一个标签，遇到行结束符之前，存在字符，content的值为这些字符串。
标签可以是开始标签，也可以是结束标签。
（2）startDocument()方法
文档启动的时候调用。
（3）endDocument()方法
解析器到达文档结尾时调用。
（4）startElement(name, attrs)方法
遇到XML开始标签时调用，name是标签的名字，attrs是标签的属性值字典。
（5）endElement(name)方法
遇到XML结束标签时调用。
在CODE上查看代码片派生到我的代码片
#coding=utf-8
#!/usr/bin/python
import xml.sax
class CountryHandler(xml.sax.ContentHandler):
def __init__(self):
self.CurrentData = ""
self.rank = ""
self.year = ""
self.gdppc = ""
self.neighborname = ""
self.neighbordirection = ""
# 元素开始事件处理
def startElement(self, tag, attributes):
self.CurrentData = tag
if tag == "country":
print "*****Country*****"
name = attributes["name"]
print "name:", name
elif tag == "neighbor":
name = attributes["name"]
direction = attributes["direction"]
print name, "->", direction
# 元素结束事件处理
def endElement(self, tag):
if self.CurrentData == "rank":
print "rank:", self.rank
elif self.CurrentData == "year":
print "year:", self.year
elif self.CurrentData == "gdppc":
print "gdppc:", self.gdppc
self.CurrentData = ""
# 内容事件处理
def characters(self, content):
if self.CurrentData == "rank":
self.rank = content
elif self.CurrentData == "year":
self.year = content
elif self.CurrentData == "gdppc":
self.gdppc = content
if __name__ == "__main__":
# 创建一个 XMLReader
parser = xml.sax.make_parser()
# turn off namepsaces
parser.setFeature(xml.sax.handler.feature_namespaces, 0)
# 重写 ContextHandler
Handler = CountryHandler()
parser.setContentHandler(Handler)
parser.parse("country.xml")
运行结果：
4、libxml2和lxml解析xml
libxml2是使用C语言开发的xml解析器，是一个基于MIT License的免费开源软件，多种编程语言都有基于它的实现，python中的libxml2模块有点小不足的是：xpathEval()接口不支持类似模板的用法，但不影响使用，因libxml2采用C语言开发的，因此在使用API接口的方式上难免会有点不适应。
在CODE上查看代码片派生到我的代码片
#!/usr/bin/python
#coding=utf-8
import libxml2
doc = libxml2.parseFile("country.xml")
for book in doc.xpathEval('//country'):
if book.content != "":
print "----------------------"
print book.content
for node in doc.xpathEval("//country/neighbor[@name = 'Colombia']"):
print node.name, (node.properties.name, node.properties.content)
doc.freeDoc()
lxml是以libxml2为基础采用python语言开发的，从使用层面上说比lxml更适合python开发者，且xpath()接口支持类似模板的用法。
在CODE上查看代码片派生到我的代码片
#!/usr/bin/python
#coding=utf-8
import lxml.etree
doc = lxml.etree.parse("country.xml")
for node in doc.xpath("//country/neighbor[@name = $name]", name = "Colombia"):
print node.tag, node.items()
for node in doc.xpath("//country[@name = $name]", name = "Singapore"):
print node.tag, node.items()
三、总结
（1）Python中XML解析可用的类库或模块有xml、libxml2 、lxml 、xpath等，需要深入了解的还需参考相应的文档。
（2）每一种解析方式都有自己的优点和缺点，选择前可以综合各个方面的性能考虑。
（3）若有不足，请留言，在此先感谢！
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