is not something we’re that familiar with, with our warm helper Wikipedia, it appears to me that XML is a set of markup language for data storing and processing. It shares similarity with html to me at first glance, so maybe it’s not that scary?…

XML is a generalized way of describing hierarchical structured data. It contains elements that are delimited by start and end tags. here follows a example:

<?xml version='1.0' encoding='utf-8'?>
<feed xmlns='http://www.w3.org/2005/Atom' xml:lang='en'>
  <title>dive into mark</title>
  ...
  <link rel='self' type='application/atom+xml' href='http://diveintomark.org/feed/'/>
  <entry>
    <author>
    <name>Mark</name>
    ...
  </entry>
  ...
</feed>

note that the xmlns is important, it declares that the feed element plus all its child elements are in the http://www.w3.org/2005/Atom namespace.

parsing and generating with ElementTree API

The sample we use is a ‘Atom feed’, and the root element is required to be feed element. We can parse the xml with the ElementTree library. See MANUAL HERE.

>>>import xml.etree.ElementTree as etree
>>>tree = etree.parse('sourcefile/examples.xml')
>>>root = tree.getroot()
>>>root
<Element '{http://www.w3.org/2005/Atom}feed' at 0x04934A20>

The parse function serves as the main entry point, it parses the entire document and returns an object which represents the entire file (or file-like object), then we use getroot() to get the root element.

As said above, the namespace is http://www.w3.org/2005/Atom, so the element, the combination of its namespace and tag name (local name) writes this way.

As an Element, root has a tag and a dictionary of attributes, it also has children nodes over which we can iterate

print(root.tag)
for child in root:
    print(child)

I believe more useful methods maybe findall(),find(), get() and the relatively new one iter()

Note that findall only finds elements that are direct children (sorry, not grandchildren), but iter() iterates recursively over its subtrees:

ns = '{http://www.w3.org/2005/Atom}'
for link in root.iter('{}link'.format(ns)):
    print(link.attrib)

for category in root.findall('{}link'.format(ns)):
    print(category.get('href'))

for entry in root.findall('{}entry'.format(ns)):
    print(entry.find('{}title'.format(ns)).text)

find and findall gets its child element, while get gets the attributes

After consulting the manual, I found that:

A better way to search the namespaced XML example is to create a dictionary with your own prefixes and use those in the search functions.

So, it turns out in this way¹

ns = { 'default': 'http://www.w3.org/2005/Atom' }
for entry in root.findall('default:entry',ns):
    print(entry.find('default:title',ns).text)

When you try to generate new xml file, the ElementTree can also help:

>>> import xml.etree.ElementTree as etree
>>> new_feed = etree.Element('{http://www.w3.org/2005/Atom}feed',
... attrib={'{http://www.w3.org/XML/1998/namespace}lang': 'en'})
>>> print(etree.tostring(new_feed))
<ns0:feed xmlns:ns0='http://www.w3.org/2005/Atom' xml:lang='en'/>

You can also use SubElement to create child element of an existing element.

But the built-in library is somewhat insufficient to handle full XPath and the it employs “draconian error handling.” as required by specification. The author suggests using lxml library to enjoy a fuller support and can use custom XMl parser to make up some of the wellformedness error.