关于xml文件，python可以用两种方式来进行解析，DOM（Document object model）和SAX（simple API for xml）。其中DOM是将xml数据加载到内存中形成一个树，通过对树的操作来操作xml，之后可以通过DOM提供的函数对文档进行读取和修改。SAX是基于事件驱动的API，包括两个部分：解析器和事件处理器。首先对xml数据进行解析，过程中会触发事件：开始事件start_element、 结束事件end_element 、数据char_data 。然后事件处理器会进行处理。
如：当SAX在解析一个节点时<li><a href="/python">Python</a></li> 会产生三个事件：
2.1 start_element事件，分别读取<li>、<a href="/python">
2.2 end_element事件，分别读取</a>、</li>
2.3 char_data事件、读取Python
下面要用到的xml文件：

<collection shelf="New Arrivals">
<movie title="Enemy Behind">
   <type>War, Thriller</type>
   <format>DVD</format>
   <year>2003</year>
   <rating>PG</rating>
   <stars>10</stars>
   <description>Talk about a US-Japan war</description>
</movie>
<movie title="Transformers">
   <type>Anime, Science Fiction</type>
   <format>DVD</format>
   <year>1989</year>
   <rating>R</rating>
   <stars>8</stars>
   <description>A schientific fiction</description>
</movie>
   <movie title="Trigun">
   <type>Anime, Action</type>
   <format>DVD</format>
   <episodes>4</episodes>
   <rating>PG</rating>
   <stars>10</stars>
   <description>Vash the Stampede!</description>
</movie>
<movie title="Ishtar">
   <type>Comedy</type>
   <format>VHS</format>
   <rating>PG</rating>
   <stars>2</stars>
   <description>Viewable boredom</description>
</movie>
</collection>

使用Dom解析xml文件：

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("movies.xml")
collection = DOMTree.documentElement
if collection.hasAttribute("shelf"):
   print ("Root element : %s" % collection.getAttribute("shelf"))

# 在集合中获取所有电影
movies = collection.getElementsByTagName("movie")

# 打印每部电影的详细信息
for movie in movies:
   print ("*****Movie*****")
   if movie.hasAttribute("title"):
      print ("Title: %s" % movie.getAttribute("title"))

   type = movie.getElementsByTagName('type')[0]
   print ("Type: %s" % type.childNodes[0].data)
   format = movie.getElementsByTagName('format')[0]
   print ("Format: %s" % format.childNodes[0].data)
   rating = movie.getElementsByTagName('rating')[0]
   print ("Rating: %s" % rating.childNodes[0].data)
   description = movie.getElementsByTagName('description')[0]
   print ("Description: %s" % description.childNodes[0].data)

结果如下：

Root element : New Arrivals
*****Movie*****
Title: Enemy Behind
Type: War, Thriller
Format: DVD
Rating: PG
Description: Talk about a US-Japan war
*****Movie*****
Title: Transformers
Type: Anime, Science Fiction
Format: DVD
Rating: R
Description: A schientific fiction
*****Movie*****
Title: Trigun
Type: Anime, Action
Format: DVD
Rating: PG
Description: Vash the Stampede!
*****Movie*****
Title: Ishtar
Type: Comedy
Format: VHS
Rating: PG
Description: Viewable boredom

Dom解析xml为树结构：

Dom解析xml为树

import xml.parsers.expat

class ExParser(object):
    '''Parse roster xml'''
    def __init__(self, xml_raw):
        '''init parser and setup handlers'''
        self.parser = xml.parsers.expat.ParserCreate()

        #connect handlers
        self.parser.StartElementHandler = self.start_element
        self.parser.EndElementHandler = self.end_element
        self.parser.CharacterDataHandler = self.char_data
        self.parser.Parse(xml_raw)
        del(xml_raw)

    def start_element(self, name, attrs):
        '''Start xml element handler'''
        print ('start:'+name)

    def end_element(self, name):
        '''End xml element handler'''
        print ('end:'+name)

    def char_data(self, data):
        '''Char xml element handler'''
        print ('data is '+data)

f = open("movies.xml")
data = f.read()
parser = ExParser(data)

结果如下：（部分展示）

start:collection
data is 

start:movie
data is 

data is    
start:type
data is War, Thriller
end:type
data is 

data is    
start:format
data is DVD
end:format
data is 

data is    
start:year
data is 2003
end:year
data is 

data is    
start:rating
data is PG
end:rating
data is 

data is    
start:stars
data is 10
end:stars
data is 

data is    
start:description
data is Talk about a US-Japan war
end:description
data is 

end:movie
data is 

start:movie
data is 

data is    
start:type
data is Anime, Science Fiction
end:type
data is 

data is    
start:format
data is DVD
end:format
data is 

data is    
start:year
data is 1989
end:year
data is 

data is    
start:rating
data is R
end:rating
data is 

data is    
start:stars
data is 8
end:stars
data is 

data is    
start:description
data is A schientific fiction
end:description
data is 

end:movie
data is 

。。。。。。。。。
。。。。。。。。。
end:collection

参考资料：
Python的expat库可以动态解析
python使用expat解析xml