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# ElementTree vs SAX and DOM

SAX (simple API for XML) It functions as a stream parser, with an event-driven API.

DOM (Document Object Model) It reads the XML into memory and converts it to objects that can be accessed with Python.

ElementTree

  • ElementTree is much easier to use, because it represents an XML tree (basically) as a structure of lists, and attributes are represented as dictionaries.
  • ElementTree needs much less memory for XML trees than DOM (and thus is faster), and the parsing overhead via (凭借) iterparse is comparable to SAX. Additionally, iterparse returns partial structures, and you can keep memory usage constant during parsing by discarding the structures as soon as you process them.
  • ElementTree, as in Python 2.5, has only a small feature set compared to full-blown XML libraries, but it’s enough for many applications. If you need a validating parser or complete XPath support, lxml is the way to go. For a long time, it used to be quite unstable, but I haven’t had any problems with it since 2.1.
  • ElementTree deviates (脱离) from DOM, where nodes have access to their parent and siblings. Handling actual documents rather than data stores is also a bit cumbersome (笨重的，难处理的）, because text nodes aren’t treated as actual nodes. In the XML snippet

# SAX

movies.xml

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<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>

saxparser.py

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import xml.sax


class MovieHandler(xml.sax.ContentHandler):
    def __init__(self):
        self.CurrentData = ""
        self.type = ""
        self.format = ""
        self.year = ""
        self.rating = ""
        self.stars = ""
        self.description = ""

    # 元素开始调用
    def startElement(self, tag, attributes):
        self.CurrentData = tag
        if tag == "movie":
            print("*****Movie*****")
            title = attributes["title"]
            print("Title:", title)

    # 元素结束调用
    def endElement(self, tag):
        if self.CurrentData == "type":
            print("Type:", self.type)
        elif self.CurrentData == "format":
            print("Format:", self.format)
        elif self.CurrentData == "year":
            print("Year:", self.year)
        elif self.CurrentData == "rating":
            print("Rating:", self.rating)
        elif self.CurrentData == "stars":
            print("Stars:", self.stars)
        elif self.CurrentData == "description":
            print("Description:", self.description)
        self.CurrentData = ""

    # 读取字符时调用
    def characters(self, content):
        if self.CurrentData == "type":
            self.type = content
        elif self.CurrentData == "format":
            self.format = content
        elif self.CurrentData == "year":
            self.year = content
        elif self.CurrentData == "rating":
            self.rating = content
        elif self.CurrentData == "stars":
            self.stars = content
        elif self.CurrentData == "description":
            self.description = content


if __name__ == "__main__":

    # 创建一个 XMLReader
    parser = xml.sax.make_parser()
    # 关闭命名空间
    parser.setFeature(xml.sax.handler.feature_namespaces, 0)

    # 重写 ContextHandler
    Handler = MovieHandler()
    parser.setContentHandler(Handler)

    parser.parse("movies.xml")

# DOM

domparser.py

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import xml.dom.minidom

DOMTree = xml.dom.minidom.parse("movies.xml")
collection = DOMTree.documentElement

if collection.hasAttribute("shelf"):
    print("root element : {}".format(collection.getAttribute("shelf")))

movies = collection.getElementsByTagName("movie")

for movie in movies:
    print("***movie***")
    if movie.hasAttribute("title"):
        print("title:{}".format(movie.getAttribute("title")))
    type = movie.getElementsByTagName('type')[0]
    print('type:{}'.format(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)

# ElementTree

etreeparser.py

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import xml.etree.ElementTree as ET
tree = ET.parse('movies.xml')
root = tree.getroot()
tag = root.tag
attrib = root.attrib
print("root:{0},shelf:{1}".format(tag, attrib.get('shelf')))

for child in root:
    print(child.tag, child.attrib)
    title = child.get('title')
    format = child.find('format').text
    rating = child.find('rating').text
    stars = child.find('stars').text
    description = child.find('description').text
    print('***movie***')
    print("title:{}".format(title))
    print("type:{}".format(format))

# root:collection,shelf:New Arrivals
# movie {'title': 'Enemy Behind'}
# ***movie***
# title:Enemy Behind
# type:DVD
# movie {'title': 'Transformers'}
# ***movie***
# title:Transformers
# type:DVD
# movie {'title': 'Trigun'}
# ***movie***
# title:Trigun
# type:DVD
# movie {'title': 'Ishtar'}
# ***movie***
# title:Ishtar
# type:VHS

Edited on