Python XML parsing

Python XML parsing

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What is XML?

XML refers to the extensible markup language (e X tensible M arkup L anguage). You can take the XML tutorial from this site

XML is designed to transfer and store data.

XML is a set of rules that define semantic tags that divide documents into parts and identify them.

It is also a meta-tag language, which defines the synth language used to define other semantic, structured markup languages related to a particular domain.

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Python's analysis of XML

Common XML programming interfaces are DOM and SAX, which handle XML files in different ways and, of course, in different situations.

python has three ways to resolve XML, SAX, DOM, and ElementTree:

1.SAX (simple API for XML )

The pyhton standard library contains SAX parsers, which use an event-driven model to process XML files by triggering events one by one during the resolution of XML and calling user-defined callback functions.

2.DOM(Document Object Model)

The XML data is parsed into a tree in memory, and the XML is operated by the operation of the tree.

3.ElementTree (Element Tree)

ElementTree is like a lightweight DOM with a convenient and friendly API. Code availability is good, fast, and consumes less memory.

Note: Because doM needs to map XML data to the tree in memory, one is slower, the other is memory-consuming, while SAX streams XML files faster and uses less memory, but requires the user to implement a callback function.

The XML instance file movies used in this section .xml as follows:

<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>

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python uses SAX to resolve xml

SAX is an event-driven API.

Parsing an XML document with SAX involves two parts: the parser and the event processor.

The parser is responsible for reading the XML document and sending events to the event processor, such as the element starting to end the event with the element;

The event handler, on the other hand, is responsible for handling the transmitted XML data accordingly.

• 1, large-scale document processing;
• 2, only need part of the file, or just get specific information from the file.
• 3, want to build their own object model.

Using sax in python to handle xml starts with the introduction of the parse function in xml.sax and contentHandler in xml.sax.handler.

Introduction to the ContentHandler class approach

Characters (content) method

Timing of call:

Starting with the line, there are characters before the label is encountered, and the value of content is these strings.

From one label, before the next label is encountered, there are characters, and the value of content is these strings.

From a label, before encountering a line end character, there are characters, and the value of content is these strings.

A label can be a start label or an end label.

StartDocument() method

Called when the document starts.

EndDocument() method

The parser is called when it reaches the end of the document.

StartElement (name, attrs) method

When an XML start label is called, name is the name of the label and attrs is the property value dictionary of the label.

EndElement (name) method

Called when an XML end label is encountered.

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make_parser method

The following method creates a new parser object and returns it.

xml.sax.make_parser( [parser_list] )

Description of the parameters:

• parser_list - optional parameters, parser list

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Parser method

Here's how to create an SAX parser and parse the xml document:

xml.sax.parse( xmlfile, contenthandler[, errorhandler])

Description of the parameters:

• xmlfile - xml file name
• Contenthandler - Must be a ContentHandler object
• Errorhandler - If this parameter is specified, the errorhandler must be an SAX ErrorHandler object

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ParseString method

The parseString method creates an XML parser and parses the xml string:

xml.sax.parseString(xmlstring, contenthandler[, errorhandler])

Description of the parameters:

• xmlstring - xml string
• Contenthandler - Must be a ContentHandler object
• Errorhandler - If this parameter is specified, the errorhandler must be an SAX ErrorHandler object

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Python parses XML instances

#coding=utf-8
#!/usr/bin/python

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 = ""

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

   # 元素结束事件处理
   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 = ""

   # 内容事件处理
   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()
   # turn off namepsaces
   parser.setFeature(xml.sax.handler.feature_namespaces, 0)

   # 重写 ContextHandler
   Handler = MovieHandler()
   parser.setContentHandler( Handler )
   
   parser.parse("movies.xml")

The above code executes as follows:

*****Movie*****
Title: Enemy Behind
Type: War, Thriller
Format: DVD
Year: 2003
Rating: PG
Stars: 10
Description: Talk about a US-Japan war
*****Movie*****
Title: Transformers
Type: Anime, Science Fiction
Format: DVD
Year: 1989
Rating: R
Stars: 8
Description: A schientific fiction
*****Movie*****
Title: Trigun
Type: Anime, Action
Format: DVD
Rating: PG
Stars: 10
Description: Vash the Stampede!
*****Movie*****
Title: Ishtar
Type: Comedy
Format: VHS
Rating: PG
Stars: 2
Description: Viewable boredom

For the full SAX API documentation, please refer to Python SAX APIs

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Use xml.dom to resolve xml

Document Object Model, or DOM, is the standard programming interface recommended by the W3C organization to handle extensable labeling languages.

When a DOM parser parses an XML document, it reads the entire document at once, keeps all the elements in the document in a tree structure in memory, and then you can use the different functions provided by the DOM to read or modify the contents and structure of the document, or you can write the modified contents to the xml file.

In python, the x ml file is parsed with x ml.dom.minidom, as follows:

#coding=utf-8
#!/usr/bin/python

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

The results of the above procedures are as follows:

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

For the complete DOM API documentation, check out Python DOM APIs.