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Posts Tagged ‘xml writing’

Write XML to file

April 4, 2011 2 comments

Problem

I wanted to create an XML file. The file was simple but I wanted to avoid producing it with “print” commands. Which API should be used for this purpose? The produced XML should be human readable, i.e. pretty printed (indented).

Solution

This post is based on the thread Best XML writing tool for Python.

(1) elementtree.SimpleXMLWriter (no indenting)

The SimpleXMLWriter module contains a simple helper class for applications that need to generate well-formed XML data. The interface is very simple:

#!/usr/bin/env python

from elementtree.SimpleXMLWriter import XMLWriter
import sys

w = XMLWriter(sys.stdout)
html = w.start("html")

w.start("head")
w.element("title", "my document")
w.element("meta", name="generator", value="my application 1.0")
w.end()

w.start("body")
w.element("h1", "this is a heading")
w.element("p", "this is a paragraph")

w.start("p")
w.data("this is ")
w.element("b", "bold")
w.data(" and ")
w.element("i", "italic")
w.data(".")
w.end("p")

w.close(html)

However, the output is not indented and as I saw, this feature is missing :( Here is the output of the code above:

<html><head><title>my document</title><meta name="generator" value="my application 1.0" /></head><body><h1>this is a heading</h1><p>this is a paragraph</p><p>this is <b>bold</b> and <i>italic</i>.</p></body></html>

If we prettify it, it will look like this:

<?xml version="1.0"?>
<html>
  <head>
    <title>my document</title>
    <meta name="generator" value="my application 1.0"/>
  </head>
  <body>
    <h1>this is a heading</h1>
    <p>this is a paragraph</p>
    <p>this is <b>bold</b> and <i>italic</i>.</p>
  </body>
</html>

You can install elementtree from PyPI.

(2) lxml.etree (can do indenting)

This is what I chose for my project. This API is also very easy to use and it can do indenting. Documentation is here.

Example:

#!/usr/bin/env python

from lxml import etree as ET

root = ET.Element('background')
starttime = ET.SubElement(root, 'starttime')
hour = ET.SubElement(starttime, 'hour')
hour.text = '00'
minute = ET.SubElement(starttime, 'minute')
minute.text = '00'
second = ET.SubElement(starttime, 'second')
second.text = '01'

print ET.tostring(root, pretty_print=True, xml_declaration=True)
# write to file:
# tree = ET.ElementTree(root)
# tree.write('output.xml', pretty_print=True, xml_declaration=True)

Output:

<?xml version='1.0' encoding='ASCII'?>
<background>
  <starttime>
    <hour>00</hour>
    <minute>00</minute>
    <second>01</second>
  </starttime>
</background>

Installation:
On PyPI, you can find lxml here. However, you will have to install some additional packages too:

sudo apt-get install libxml2-dev
sudo apt-get install libxslt-dev
# until Ubuntu 10.10:
sudo apt-get install python2.6-dev
# from Ubuntu 11.04:
sudo apt-get install python2.7-dev

Then, you can install the library with “sudo pip install lxml“.

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