What is XML?
XML refers to eXtensible Markup Language. You can learn XML tutorials through this site
XML is designed to transmit and store data.
XML is a set of rules that define semantic markup that divides a document into components and identifies those components.
It is also a meta-markup language, that is, it defines a syntactic language used to define other semantic and structured markup languages related to specific fields.
Python’s parsing of XML
Common XML programming interfaces include DOM and SAX. These two interfaces process XML files in different ways, and of course the usage scenarios are also different.
Python has three methods to parse XML, SAX, DOM, and ElementTree:
1.SAX (simple API for XML)
pyhton The standard library contains a SAX parser. SAX uses an event-driven model, through the process of parsing XML Trigger events one by one and call user-defined callback functions to process XML files.
2.DOM (Document Object Model)
parses XML data into a tree in memory, and operates XML by operating on the tree.
3.ElementTree (Element Tree)
ElementTree is like a lightweight DOM with a convenient and friendly API. The code has good usability, is fast, and consumes less memory.
Note: Because DOM needs to map XML data to a tree in memory, it is relatively slow and consumes more memory. SAX streaming reading of XML files is faster and takes up less memory, but requires the user to implement a callback function. (handler).
The content of the XML example file movies.xml used in this chapter is as follows:
< type>War, Thriller
< ;description>A schientific fiction
python use SAX parses xml SAX is an event-driven API. Using SAX to parse XML documents involves two parts: the parser and the event handler. The parser is responsible for reading the XML document and sending events to the event processor, such as element start and element end events; The event processor is responsible for responding to the event and processing the passed XML data. 1. Process large files; 2. Only need part of the file, or only need specific information from the file. 3. When you want to build your own object model. To use sax to process xml in python, you must first introduce the parse function in xml.sax and the ContentHandler in xml.sax.handler. ContentHandler class method introduction characters(content) method Calling timing: Starting from the line, before encountering the label, there are characters, and the value of content is these strings. From one label, there are characters before encountering the next label, and the value of content is these strings. From a label, there are characters before encountering the line terminator, and the value of content is these strings. The tag can be a start tag or an end tag. startDocument() method is called when the document is started. endDocument() method is called when the parser reaches the end of the document. The startElement(name, attrs) method is called when an XML start tag is encountered. name is the name of the tag, and attrs is the attribute value dictionary of the tag. endElement(name) method is called when an XML end tag is encountered. make_parser method The following method creates a new parser object and returns it. xml.sax.make_parser([parser_list]) Parameter description: parser_list - optional parameters, parser list parser method The following method creates a SAX parser device and Parse xml document: xml.sax.parse(xmlfile, contenthandler[, errorhandler]) Parameter description: xmlfile - xml file name contenthandler - must be a ContentHan dler object errorhandler - If this parameter is specified, errorhandler must be a SAX ErrorHandler object parseString method parseString method creates an XML parser and parses an xml string: xml.sax.parseString(xmlstring, contenthandler [, errorhandler]) Parameter description: xmlstring - xml string contenthandler - must be a ContentHandler object errorhandler - if this parameter is specified, errorhandler must be a SAX ErrorHandler object Python Parse XML instance #!/usr/bin/python import xml.sax class MovieHandler( xml.sax.ContentHandler ): def __init__(self): self .CurrentData = "" self.type . "" self.description = "" # Element start event processing def startElement(self, tag, attributes): self.CurrentData = tag if tag == "movie": print "***** Movie*****" Movie**** if self. CurrentData == "type": CurrentData == " year": . 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") 以上代码执行结果如下： *****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 完整的 SAX API 文档请查阅Python SAX APIs 使用xml.dom解析xml 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，实例如下： #!/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 execution result of the above program is 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
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