CSCI/CMPE 4341 Topic: CSCI/CMPE 4341 Topic: Programming in PythonProgramming in Python
Chapter 9: Python XML ProcessingChapter 9: Python XML Processing
Xiang Lian
The University of Texas – Pan American
Edinburg, TX 78539
1
Objectives
• In this chapter, you will:– Understand XML
– Become familiar with the types of markup languages created with XML
– Learn to create XML markup programmatically
– Use the Document Object Model (DOM) to manipulate XML documents
– Explore ElementTree package to retrieve data from XML documents
2
Introduction
• XML developed by World Wide Consortium’s (W3C’s) XML Working Group (1996)
• XML portable, widely supported, open technology for describing data
• XML quickly becoming standard for data exchange between applications
3
XML Documents
• XML documents end with .xml extension
• XML marks up data using tags, which are names enclosed in angle brackets – <tag> elements </tag>
– Elements: individual units of markup (i.e., everything included between a start tag and its corresponding end tag)
– Nested elements form hierarchies
– Root element contains all other document elements
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Outline5
article.xml
<?xml version = "1.0"?> <!-- Fig. 15.1: article.xml --><!-- Article structured with XML. --> <article>
<title>Simple XML</title>
<date>December 21, 2001</date>
<author><firstName>John</firstName><lastName>Doe</lastName>
</author>
<summary>XML is pretty easy.</summary>
<content>In this chapter, we present a wide variety of examplesthat use XML.
</content> </article>
Optional XML declaration includes version information parameter
XML comments delimited by <!– and -->
Root element contains all other document elements
End tag has format </start tag name>
XML Document
• View XML documents– Any text editor• Internet Explorer, Notepad, Visual Studio, etc.
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Minus sign
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Outline7
letter.xml
1 <?xml version = "1.0"?>2 3 <!-- Fig. 15.3: letter.xml -->4 <!-- Business letter formatted with XML. -->5 6 <letter>7 <contact type = "from">8 <name>Jane Doe</name>9 <address1>Box 12345</address1>10 <address2>15 Any Ave.</address2>11 <city>Othertown</city>12 <state>Otherstate</state>13 <zip>67890</zip>14 <phone>555-4321</phone>15 <flag gender = "F" />16 </contact>17 18 <contact type = "to">19 <name>John Doe</name>20 <address1>123 Main St.</address1>21 <address2></address2>22 <city>Anytown</city>23 <state>Anystate</state>24 <zip>12345</zip>25 <phone>555-1234</phone>26 <flag gender = "M" />27 </contact>28 29 <salutation>Dear Sir:</salutation>30
Root element letterChild element contactAttribute (name-value pair)
Empty elements do not contain character data
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Outline8
letter.xml
31 <paragraph>It is our privilege to inform you about our new32 database managed with <technology>XML</technology>. This33 new system allows you to reduce the load on34 your inventory list server by having the client machine35 perform the work of sorting and filtering the data.36 </paragraph>37 38 <paragraph>Please visit our Web site for availability39 and pricing.40 </paragraph>41 42 <closing>Sincerely</closing>43 44 <signature>Ms. Doe</signature>45 </letter>
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XML Namespaces
• Provided for unique identification of XML elements
• Namespace prefixes identify namespace to which an element belongs<Xiang:CSCI/CMPE4341>
Topic: Programming in Python
</Xiang:CSCI/CMPE4341>
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Outline10
namespace.xml
1 <?xml version = "1.0"?>2 3 <!-- Fig. 15.4: namespace.xml -->4 <!-- Demonstrating namespaces. -->5 6 <text:directory xmlns:text = "http://www.deitel.com/ns/python1e"7 xmlns:image = "http://www.deitel.com/images/ns/120101">8 9 <text:file filename = "book.xml">10 <text:description>A book list</text:description>11 </text:file>12 13 <image:file filename = "funny.jpg">14 <image:description>A funny picture</image:description>15 <image:size width = "200" height = "100" />16 </image:file>17 18 </text:directory>
Attribute xmlns creates namespace prefixNamespace prefix bound to an URI
Uses prefix text to describe element file
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Outline11
defaultnamespace.xml
1 <?xml version = "1.0"?>2 3 <!-- Fig. 15.5: defaultnamespace.xml -->4 <!-- Using default namespaces. -->5 6 <directory xmlns = "http://www.deitel.com/ns/python1e"7 xmlns:image = "http://www.deitel.com/images/ns/120101">8 9 <file filename = "book.xml">10 <description>A book list</description>11 </file>12 13 <image:file filename = "funny.jpg">14 <image:description>A funny picture</image:description>15 <image:size width = "200" height = "100" />16 </image:file>17 18 </directory>
Creates default namespace by binding URI to attribute xmlns without prefix
Element without prefix defined in default namespace
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Document Object Model (DOM)
• DOM parser retrieves data from XML document
• Hierarchical tree structure called a DOM tree– Each component of an XML document represented
as a tree node– Parent nodes contain child nodes– Sibling nodes have same parent– Single root (or document) node contains all other
document nodes
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Example of Document Object Model (DOM)
article
title
author
summary
contents
lastName
firstName
date
Processing XML in Python
• Python packages for XML support– 4DOM and xml.sax
– Generating XML dynamically similar to generating HTML
– Python scripts can use print statements or XSLT to output XML
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Outline15
names.txt
O'Black, JohnGreen, SueRed, BobBlue, MaryWhite, MikeBrown, JaneGray, Bill
Fig. 16.1 Text file names.txt used in Fig. 16.2.
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Outline16
fig16_02.py
#!c:\Python\python.exe# Fig. 16.2: fig16_02.py# Marking up a text file's data as XML. import sys
# write XML declaration and processing instructionprint ("""<?xml version = "1.0"?> """)
# open data filetry:
file = open( "names.txt", "r" )except IOError:
sys.exit( "Error opening file" ) print ("<contacts>") # write root element # list of tuples: ( special character, entity reference )replaceList = [ ( "&", "&" ),
( "<", "<" ),( ">", ">" ),( '"', """ ),( "'", "'" ) ]
# replace special characters with entity referencesfor currentLine in file.readlines():
for oldValue, newValue in replaceList:currentLine = currentLine.replace( oldValue, newValue )
Print XML declaration
Open text file if it exists
Print root element
List of special characters and their entity references
Replace special characters with entity references
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Outline17
fig16_02.py
# extract lastname and firstnamelast, first = currentLine.split( ", " )first = first.strip() # remove carriage return
# write contact elementprint (""" <contact>
<LastName>%s</LastName><FirstName>%s</FirstName>
</contact>""" % ( last, first )) file.close() print ("</contacts>")
Extract first and last nameRemove carriage return
Print contact element
Print root’s closing tag
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XML Processing Packages
• Third-party package 4DOM, included with package PyXML, complies with W3C’s DOM Recommendation
• xml.sax, included with Python, contains classes and functions for SAX-based parsing
• 4XSLT, located in package 4Suite, contains an XSLT processor for transforming XML documents into other text-based formats
• import xml.etree.ElementTree
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Outline19
article2.xml
<?xml version = "1.0"?> <!-- Fig. 16.5: article2.xml --><!-- Article formatted with XML --> <article>
<title>Simple XML</title>
<date>December 19, 2001</date>
<author><firstName>Jane</firstName><lastName>Doe</lastName>
</author>
<summary>XML is easy.</summary>
<content>Once you have mastered XHTML, XML is learnedeasily. Remember that XML is not for displayinginformation but for managing information.</content>
</article>
XML document used by fig16_04.py
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Outline20
fig16_04.py
# Fig. 16.4: fig16_04.py# Using 4DOM to traverse an XML Document. import sysimport xml.etree.ElementTree as etree # open XML filetry:
tree = etree.parse("article2.xml")except IOError:
sys.exit( "Error opening file" ) # get root elementrootElement = tree.getroot()print ("Here is the root element of the document: %s" % \
rootElement.tag)
# traverse all child nodes of root elementprint ("The following are its child elements:" )
for node in rootElement:print (node)
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Outline
fig16_04.py
# get first child node of root elementchild = rootElement[0]print ("\nThe first child of root element is:", child.tag)print ("whose next sibling is:" )
# get next sibling of first childsibling = rootElement[1] print (sibling.tag)
print ('Value of "%s" is:' % sibling.tag, end="")print (sibling.text)