=======================
The lxml.etree Tutorial
=======================
.. meta::
:description: The lxml tutorial on XML that feels like Python
:keywords: lxml, etree, tutorial, ElementTree, Python, XML, HTML
:Author:
Stefan Behnel
This tutorial briefly overviews the main concepts of the `ElementTree API`_ as
implemented by ``lxml.etree``, and some simple enhancements that make your
life as a programmer easier.
For a complete reference of the API, see the `generated API
documentation`_.
.. _`ElementTree API`: http://effbot.org/zone/element-index.htm#documentation
.. _`generated API documentation`: api/index.html
.. contents::
..
1 The Element class
1.1 Elements are lists
1.2 Elements carry attributes
1.3 Elements contain text
1.4 Using XPath to find text
1.5 Tree iteration
1.6 Serialisation
2 The ElementTree class
3 Parsing from strings and files
3.1 The fromstring() function
3.2 The XML() function
3.3 The parse() function
3.4 Parser objects
3.5 Incremental parsing
3.6 Event-driven parsing
4 Namespaces
5 The E-factory
6 ElementPath
A common way to import ``lxml.etree`` is as follows::
>>> from lxml import etree
If your code only uses the ElementTree API and does not rely on any
functionality that is specific to ``lxml.etree``, you can also use (any part
of) the following import chain as a fall-back to the original ElementTree::
try:
from lxml import etree
print "running with lxml.etree"
except ImportError:
try:
# Python 2.5
import xml.etree.cElementTree as etree
print "running with cElementTree on Python 2.5+"
except ImportError:
try:
# Python 2.5
import xml.etree.ElementTree as etree
print "running with ElementTree on Python 2.5+"
except ImportError:
try:
# normal cElementTree install
import cElementTree as etree
print "running with cElementTree"
except ImportError:
try:
# normal ElementTree install
import elementtree.ElementTree as etree
print "running with ElementTree"
except ImportError:
print "Failed to import ElementTree from any known place"
To aid in writing portable code, this tutorial makes it clear in the examples
which part of the presented API is an extension of lxml.etree over the
original `ElementTree API`_, as defined by Fredrik Lundh's `ElementTree
library`_.
.. _`ElementTree library`: http://effbot.org/zone/element-index.htm
The Element class
=================
An ``Element`` is the main container object for the ElementTree API. Most of
the XML tree functionality is accessed through this class. Elements are
easily created through the ``Element`` factory::
>>> root = etree.Element("root")
The XML tag name of elements is accessed through the ``tag`` property::
>>> print root.tag
root
Elements are organised in an XML tree structure. To create child elements and
add them to a parent element, you can use the ``append()`` method::
>>> root.append( etree.Element("child1") )
However, this is so common that there is a shorter and much more efficient way
to do this: the ``SubElement`` factory. It accepts the same arguments as the
``Element`` factory, but additionally requires the parent as first argument::
>>> child2 = etree.SubElement(root, "child2")
>>> child3 = etree.SubElement(root, "child3")
To see that this is really XML, you can serialise the tree you have created::
>>> print etree.tostring(root, pretty_print=True),
<root>
<child1/>
<child2/>
<child3/>
</root>
Elements are lists
------------------
To make the access to these subelements as easy and straight forward as
possible, elements behave like normal Python lists::
>>> child = root[0]
>>> print child.tag
child1
>>> print len(root)
3
>>> root.index(root[1]) # lxml.etree only!
1
>>> children = list(root)
>>> for child in root:
... print child.tag
child1
child2
child3
>>> root.insert(0, etree.Element("child0"))
>>> start = root[:1]
>>> end = root[-1:]
>>> print start[0].tag
child0
>>> print end[0].tag
child3
>>> root[0] = root[-1] # this moves the element!
>>> for child in root:
... print child.tag
child3
child1
child2
Prior to ElementTree 1.3 and lxml 2.0, you could also check the truth value of
an Element to see if it has children, i.e. if the list of children is empty.
This is no longer supported as people tend to find it surprising that a
non-None reference to an existing Element can evaluate to False. Instead, use
``len(element)``, which is both more explicit and less error prone.
Note in the examples that the last element was *moved* to a different position
in the last example. This is a difference from the original ElementTree (and
from lists), where elements can sit in multiple positions of any number of
trees. In lxml.etree, elements can only sit in one position of one tree at a
time.
If you want to *copy* an element to a different position, consider creating an
independent *deep copy* using the ``copy`` module from Python's standard
library::
>>> from copy import deepcopy
>>> element = etree.Element("neu")
>>> element.append( deepcopy(root[1]) )
>>> print element[0].tag
child1
>>> print [ c.tag for c in root ]
['child3', 'child1', 'child2']
The way up in the tree is provided through the ``getparent()`` method::
>>> root is root[0].getparent() # lxml.etree only!
True
The siblings (or neighbours) of an element are accessed as next and previous
elements::
>>> root[0] is root[1].getprevious() # lxml.etree only!
True
>>> root[1] is root[0].getnext() # lxml.etree only!
True
Elements carry attributes
-------------------------
XML elements support attributes. You can create them directly in the Element
factory::
>>> root = etree.Element("root", interesting="totally")
>>> print etree.tostring(root)
<root interesting="totally"/>
Fast and direct access to these attributes is provided by the ``set()`` and
``get()`` methods of elements::
>>> print root.get("interesting")
totally
>>> root.set("interesting", "somewhat")
>>> print root.get("interesting")
somewhat
However, a very convenient way of dealing with them is through the dictionary
interface of the ``attrib`` property::
>>> attributes = root.attrib
>>> print attributes["interesting"]
somewhat
>>> print attributes.get("hello")
None
>>> attributes["hello"] = "Guten Tag"
>>> print attributes.get("hello")
Guten Tag
>>> print root.get("hello")
Guten Tag
Elements contain text
---------------------
Elements can contain text::
>>> root = etree.Element("root")
>>> root.text = "TEXT"
>>> print root.text
TEXT
>>> print etree.tostring(root)
<root>TEXT</root>
In many XML documents (*data-centric* documents), this is the only place where
text can be found. It is encapsulated by a leaf tag at the very bottom of the
tree hierarchy.
However, if XML is used for tagged text documents such as (X)HTML, text can
also appear between different elements, right in the middle of the tree::
<html><body>Hello<br/>World</body></html>
Here, the ``<br/>`` tag is surrounded by text. This is often referred to as
*document-style* or *mixed-content* XML. Elements support this through their
``tail`` property. It contains the text that directly follows the element, up
to the next element in the XML tree::
>>> html = etree.Element("html")
>>> body = etree.SubElement(html, "body")
>>> body.text = "TEXT"
>>> print etree.tostring(html)
<html><body>TEXT</body></html>
>>> br = etree.SubElement(body, "br")
>>> print etree.tostring(html)
<html><body>TEXT<br/></body></html>
>>> br.tail = "TAIL"
>>> print etree.tostring(html)
<html><body>TEXT<br/>TAIL</body></html>
The two properties ``.text`` and ``.tail`` are enough to represent any
text content in an XML document. This way, the ElementTree API does
not require any `special text nodes`_ in addition to the Element
class, that tend to get in the way fairly often (as you might know
from classic DOM_ APIs).
However, there are cases where the tail text also gets in the way.
For example, when you serialise an Element from within the tree, you
do not always want its tail text in the result (although you would
still want the tail text of its children). For this purpose, the
``tostring()`` function accepts the keyword argument ``with_tail``::
>>> print etree.tostring(br)
<br/>TAIL
>>> print etree.tostring(br, with_tail=False) # lxml.etree only!
<br/>
.. _`special text nodes`: http://www.w3.org/TR/DOM-Level-3-Core/core.html#ID-1312295772
.. _DOM: http://www.w3.org/TR/DOM-Level-3-Core/core.html
If you want to read *only* the text, i.e. without any intermediate
tags, you have to recursively concatenate all ``text`` and ``tail``
attributes in the correct order. Again, the ``tostring()`` function
comes to the rescue, this time using the ``method`` keyword::
>>> print etree.tostring(html, method="text")
TEXTTAIL
Using XPath to find text
------------------------
.. _XPath: xpathxslt.html#xpath
Another way to extract the text content of a tree is XPath_, which
also allows you to extract the separate text chunks into a list::
>>> print html.xpath("string()") # lxml.etree only!
TEXTTAIL
>>> print html.xpath("//text()") # lxml.etree only!
['TEXT', 'TAIL']
If you want to use this more often, you can wrap it in a function::
>>> build_text_list = etree.XPath("//text()") # lxml.etree only!
>>> print build_text_list(html)
['TEXT', 'TAIL']
Note that a string result returned by XPath is a special 'smart'
object that knows about its origins. You can ask it where it came
from through its ``getparent()`` method, just as you would with
Elements::
>>> texts = build_text_list(html)
>>> print texts[0]
TEXT
>>> parent = texts[0].getparent()
>>> print parent.tag
body
>>> print texts[1]
TAIL
>>> print texts[1].getparent().tag
br
You can also find out if it's normal text content or tail text::
>>> print texts[0].is_text
True
>>> print texts[1].is_text
False
>>> print texts[1].is_tail
True
While this works for the results of the ``text()`` function, lxml will
not to tell you the origin of a string value that was constructed by
the XPath functions ``string()`` or ``concat()``::
>>> stringify = etree.XPath("string()")
>>> print stringify(html)
TEXTTAIL
>>> print stringify(html).getparent()
None
Tree iteration
--------------
For problems like the above, where you want to recursively traverse the tree
and do something with its elements, tree iteration is a very convenient
solution. Elements provide a tree iterator for this purpose. It yields
elements in *document order*, i.e. in the order their tags would appear if you
serialised the tree to XML::
>>> root = etree.Element("root")
>>> etree.SubElement(root, "child").text = "Child 1"
>>> etree.SubElement(root, "child").text = "Child 2"
>>> etree.SubElement(root, "another").text = "Child 3"
>>> print etree.tostring(root, pretty_print=True),
<root>
<child>Child 1</child>
<child>Child 2</child>
<another>Child 3</another>
</root>
>>> for element in root.iter():
... print element.tag, '-', element.text
root - None
child - Child 1
child - Child 2
another - Child 3
If you know you are only interested in a single tag, you can pass its name to
``iter()`` to have it filter for you::
>>> for element in root.iter("child"):
... print element.tag, '-', element.text
child - Child 1
child - Child 2
By default, iteration yields all nodes in the tree, including
ProcessingInstructions, Comments and Entity instances. If you want to
make sure only Element objects are returned, you can pass the
``Element`` factory as tag parameter::
>>> root.append(etree.Entity("#234"))
>>> root.append(etree.Comment("some comment"))
>>> for element in root.iter():
... if isinstance(element.tag, basestring):
... print element.tag, '-', element.text
... else:
... print 'SPECIAL:', element, '-', element.text
root - None
child - Child 1
child - Child 2
another - Child 3
SPECIAL: ê - ê
SPECIAL: <!--some comment--> - some comment
>>> for element in root.iter(tag=etree.Element):
... print element.tag, '-', element.text
root - None
child - Child 1
child - Child 2
another - Child 3
>>> for element in root.iter(tag=etree.Entity):
... print element.text
ê
In lxml.etree, elements provide `further iterators`_ for all directions in the
tree: children, parents (or rather ancestors) and siblings.
.. _`further iterators`: api.html#iteration
Serialisation
-------------
Serialisation commonly uses the ``tostring()`` function that returns a
string, or the ``ElementTree.write()`` method that writes to a file or
file-like object. Both accept the same keyword arguments like
``pretty_print`` for formatted output or ``encoding`` to select a
specific output encoding other than plain ASCII::
>>> root = etree.XML('<root><a><b/></a></root>')
>>> print etree.tostring(root)
<root><a><b/></a></root>
>>> print etree.tostring(root, xml_declaration=True)
<?xml version='1.0' encoding='ASCII'?>
<root><a><b/></a></root>
>>> print etree.tostring(root, encoding='iso-8859-1')
<?xml version='1.0' encoding='iso-8859-1'?>
<root><a><b/></a></root>
>>> print etree.tostring(root, pretty_print=True),
<root>
<a>
<b/>
</a>
</root>
Note the newline that is appended at the end when pretty printing the
output.
Since lxml 2.0 (and ElementTree 1.3), the serialisation functions can
do more than XML serialisation. You can serialise to HTML or extract
the text content by passing the ``method`` keyword::
>>> root = etree.XML('<html><head/><body><p>Hello<br/>World</p></body></html>')
>>> print etree.tostring(root) # default: method = 'xml'
<html><head/><body><p>Hello<br/>World</p></body></html>
>>> print etree.tostring(root, method='xml') # same as above
<html><head/><body><p>Hello<br/>World</p></body></html>
>>> print etree.tostring(root, method='html')
<html><head></head><body><p>Hello<br>World</p></body></html>
>>> print etree.tostring(root, method='html', pretty_print=True),
<html>
<head></head>
<body><p>Hello<br>World</p></body>
</html>
>>> print etree.tostring(root, method='text')
HelloWorld
For the plain text output, serialising to a Python unicode string
might become handy. Just pass the ``unicode`` type as encoding::
>>> etree.tostring(root, encoding=unicode, method='text')
u'HelloWorld'
The ElementTree class
=====================
An ``ElementTree`` is mainly a document wrapper around a tree with a
root node. It provides a couple of methods for parsing, serialisation
and general document handling. One of the bigger differences is that
it serialises as a complete document, as opposed to a single
``Element``. This includes top-level processing instructions and
comments, as well as a DOCTYPE and other DTD content in the document::
>>> from StringIO import StringIO
>>> tree = etree.parse(StringIO('''\
... <?xml version="1.0"?>
... <!DOCTYPE root SYSTEM "test" [ <!ENTITY tasty "eggs"> ]>
... <root>
... <a>&tasty;</a>
... </root>
... '''))
>>> print tree.docinfo.doctype
<!DOCTYPE root SYSTEM "test">
>>> # lxml 1.3.4 and later
>>> print etree.tostring(tree)
<!DOCTYPE root SYSTEM "test" [
<!ENTITY tasty "eggs">
]>
<root>
<a>eggs</a>
</root>
>>> # lxml 1.3.4 and later
>>> print etree.tostring(etree.ElementTree(tree.getroot()))
<!DOCTYPE root SYSTEM "test" [
<!ENTITY tasty "eggs">
]>
<root>
<a>eggs</a>
</root>
>>> # ElementTree and lxml <= 1.3.3
>>> print etree.tostring(tree.getroot())
<root>
<a>eggs</a>
</root>
Note that this has changed in lxml 1.3.4 to match the behaviour of the
upcoming lxml 2.0. Before, both would serialise without DTD content, which
made lxml loose DTD information in an input-output cycle.
Parsing from strings and files
==============================
``lxml.etree`` supports parsing XML in a number of ways and from all
important sources, namely strings, files, URLs (http/ftp) and
file-like objects. The main parse functions are ``fromstring()`` and
``parse()``, both called with the source as first argument. By
default, they use the standard parser, but you can always pass a
different parser as second argument.
The fromstring() function
-------------------------
The ``fromstring()`` function is the easiest way to parse a string::
>>> some_xml_data = "<root>data</root>"
>>> root = etree.fromstring(some_xml_data)
>>> print root.tag
root
>>> print etree.tostring(root)
<root>data</root>
The XML() function
------------------
The ``XML()`` function behaves like the ``fromstring()`` function, but is
commonly used to write XML literals right into the source::
>>> root = etree.XML("<root>data</root>")
>>> print root.tag
root
>>> print etree.tostring(root)
<root>data</root>
The parse() function
--------------------
The ``parse()`` function is used to parse from files and file-like objects::
>>> some_file_like = StringIO("<root>data</root>")
>>> tree = etree.parse(some_file_like)
>>> print etree.tostring(tree)
<root>data</root>
Note that ``parse()`` returns an ElementTree object, not an Element object as
the string parser functions::
>>> root = tree.getroot()
>>> print root.tag
root
>>> print etree.tostring(root)
<root>data</root>
The reasoning behind this difference is that ``parse()`` returns a
complete document from a file, while the string parsing functions are
commonly used to parse XML fragments.
The ``parse()`` function supports any of the following sources:
* an open file object
* a file-like object that has a ``.read(byte_count)`` method returning
a byte string on each call
* a filename string
* an HTTP or FTP URL string
Note that passing a filename or URL is usually faster than passing an
open file.
Parser objects
--------------
By default, ``lxml.etree`` uses a standard parser with a default setup. If
you want to configure the parser, you can create a you instance::
>>> parser = etree.XMLParser(remove_blank_text=True) # lxml.etree only!
This creates a parser that removes empty text between tags while parsing,
which can reduce the size of the tree and avoid dangling tail text if you know
that whitespace-only content is not meaningful for your data. An example::
>>> root = etree.XML("<root> <a/> <b> </b> </root>", parser)
>>> print etree.tostring(root)
<root><a/><b> </b></root>
Note that the whitespace content inside the ``<b>`` tag was not removed, as
content at leaf elements tends to be data content (even if blank). You can
easily remove it in an additional step by traversing the tree::
>>> for element in root.iter("*"):
... if element.text is not None and not element.text.strip():
... element.text = None
>>> print etree.tostring(root)
<root><a/><b/></root>
See ``help(etree.XMLParser)`` to find out about the available parser options.
Incremental parsing
-------------------
``lxml.etree`` provides two ways for incremental step-by-step parsing. One is
through file-like objects, where it calls the ``read()`` method repeatedly.
This is best used where the data arrives from a source like ``urllib`` or any
other file-like object that can provide data on request. Note that the parser
will block and wait until data becomes available in this case::
>>> class DataSource:
... data = iter(["<roo", "t><", "a/", "><", "/root>"])
... def read(self, requested_size):
... try:
... return self.data.next()
... except StopIteration:
... return ""
>>> tree = etree.parse(DataSource())
>>> print etree.tostring(tree)
<root><a/></root>
The second way is through a feed parser interface, given by the ``feed(data)``
and ``close()`` methods::
>>> parser = etree.XMLParser()
>>> parser.feed("<roo")
>>> parser.feed("t><")
>>> parser.feed("a/")
>>> parser.feed("><")
>>> parser.feed("/root>")
>>> root = parser.close()
>>> print etree.tostring(root)
<root><a/></root>
Here, you can interrupt the parsing process at any time and continue it later
on with another call to the ``feed()`` method. This comes in handy if you
want to avoid blocking calls to the parser, e.g. in frameworks like Twisted,
or whenever data comes in slowly or in chunks and you want to do other things
while waiting for the next chunk.
After calling the ``close()`` method (or when an exception was raised
by the parser), you can reuse the parser by calling its ``feed()``
method again::
>>> parser.feed("<root/>")
>>> root = parser.close()
>>> print etree.tostring(root)
<root/>
Event-driven parsing
--------------------
Sometimes, all you need from a document is a small fraction somewhere deep
inside the tree, so parsing the whole tree into memory, traversing it and
dropping it can be too much overhead. ``lxml.etree`` supports this use case
with two event-driven parser interfaces, one that generates parser events
while building the tree (``iterparse``), and one that does not build the tree
at all, and instead calls feedback methods on a target object in a SAX-like
fashion.
Here is a simple ``iterparse()`` example::
>>> some_file_like = StringIO("<root><a>data</a></root>")
>>> for event, element in etree.iterparse(some_file_like):
... print "%s, %4s, %s" % (event, element.tag, element.text)
end, a, data
end, root, None
By default, ``iterparse()`` only generates events when it is done parsing an
element, but you can control this through the ``events`` keyword argument::
>>> some_file_like = StringIO("<root><a>data</a></root>")
>>> for event, element in etree.iterparse(some_file_like,
... events=("start", "end")):
... print "%5s, %4s, %s" % (event, element.tag, element.text)
start, root, None
start, a, data
end, a, data
end, root, None
Note that the text, tail and children of an Element are not necessarily there
yet when receiving the ``start`` event. Only the ``end`` event guarantees
that the Element has been parsed completely.
It also allows to ``.clear()`` or modify the content of an Element to
save memory. So if you parse a large tree and you want to keep memory
usage small, you should clean up parts of the tree that you no longer
need::
>>> some_file_like = StringIO(
... "<root><a><b>data</b></a><a><b/></a></root>")
>>> for event, element in etree.iterparse(some_file_like):
... if element.tag == 'b':
... print element.text
... elif element.tag == 'a':
... print "** cleaning up the subtree"
... element.clear()
data
** cleaning up the subtree
None
** cleaning up the subtree
If memory is a real bottleneck, or if building the tree is not desired at all,
the target parser interface of ``lxml.etree`` can be used. It creates
SAX-like events by calling the methods of a target object. By implementing
some or all of these methods, you can control which events are generated::
>>> class ParserTarget:
... events = []
... def start(self, tag, attrib):
... self.events.append(("start", tag, attrib))
... def close(self):
... return self.events
>>> parser = etree.XMLParser(target=ParserTarget())
>>> events = etree.fromstring('<root test="true"/>', parser)
>>> for event in events:
... print 'event: %s - tag: %s' % (event[0], event[1])
... for attr, value in event[2].iteritems():
... print ' * %s = %s' % (attr, value)
event: start - tag: root
* test = true
Namespaces
==========
The ElementTree API avoids `namespace prefixes`_ wherever possible and deploys
the real namespaces instead::
>>> xhtml = etree.Element("{http://www.w3.org/1999/xhtml}html")
>>> body = etree.SubElement(xhtml, "{http://www.w3.org/1999/xhtml}body")
>>> body.text = "Hello World"
>>> print etree.tostring(xhtml, pretty_print=True),
<html:html xmlns:html="http://www.w3.org/1999/xhtml">
<html:body>Hello World</html:body>
</html:html>
.. _`namespace prefixes`: http://www.w3.org/TR/xml-names/#ns-qualnames
As you can see, prefixes only become important when you serialise the result.
However, the above code becomes somewhat verbose due to the lengthy namespace
names. And retyping or copying a string over and over again is error prone.
It is therefore common practice to store a namespace URI in a global variable.
To adapt the namespace prefixes for serialisation, you can also pass a mapping
to the Element factory, e.g. to define the default namespace::
>>> XHTML_NAMESPACE = "http://www.w3.org/1999/xhtml"
>>> XHTML = "{%s}" % XHTML_NAMESPACE
>>> NSMAP = {None : XHTML_NAMESPACE} # the default namespace (no prefix)
>>> xhtml = etree.Element(XHTML + "html", nsmap=NSMAP) # lxml only!
>>> body = etree.SubElement(xhtml, XHTML + "body")
>>> body.text = "Hello World"
>>> print etree.tostring(xhtml, pretty_print=True),
<html xmlns="http://www.w3.org/1999/xhtml">
<body>Hello World</body>
</html>
Namespaces on attributes work alike::
>>> body.set(XHTML + "bgcolor", "#CCFFAA")
>>> print etree.tostring(xhtml, pretty_print=True),
<html xmlns="http://www.w3.org/1999/xhtml">
<body bgcolor="#CCFFAA">Hello World</body>
</html>
>>> print body.get("bgcolor")
None
>>> body.get(XHTML + "bgcolor")
'#CCFFAA'
You can also use XPath in this way::
>>> find_xhtml_body = etree.ETXPath( # lxml only !
... "//{%s}body" % XHTML_NAMESPACE)
>>> results = find_xhtml_body(xhtml)
>>> print results[0].tag
{http://www.w3.org/1999/xhtml}body
The E-factory
=============
The ``E-factory`` provides a simple and compact syntax for generating XML and
HTML::
>>> from lxml.builder import E
>>> def CLASS(*args): # class is a reserved word in Python
... return {"class":' '.join(args)}
>>> html = page = (
... E.html( # create an Element called "html"
... E.head(
... E.title("This is a sample document")
... ),
... E.body(
... E.h1("Hello!", CLASS("title")),
... E.p("This is a paragraph with ", E.b("bold"), " text in it!"),
... E.p("This is another paragraph, with a", "\n ",
... E.a("link", href="http://www.python.org"), "."),
... E.p("Here are some reservered characters: <spam&egg>."),
... etree.XML("<p>And finally an embedded XHTML fragment.</p>"),
... )
... )
... )
>>> print etree.tostring(page, pretty_print=True),
<html>
<head>
<title>This is a sample document</title>
</head>
<body>
<h1 class="title">Hello!</h1>
<p>This is a paragraph with <b>bold</b> text in it!</p>
<p>This is another paragraph, with a
<a href="http://www.python.org">link</a>.</p>
<p>Here are some reservered characters: <spam&egg>.</p>
<p>And finally an embedded XHTML fragment.</p>
</body>
</html>
The Element creation based on attribute access makes it easy to build up a
simple vocabulary for an XML language::
>>> from lxml.builder import ElementMaker # lxml only !
>>> E = ElementMaker(namespace="http://my.de/fault/namespace",
... nsmap={'p' : "http://my.de/fault/namespace"})
>>> DOC = E.doc
>>> TITLE = E.title
>>> SECTION = E.section
>>> PAR = E.par
>>> my_doc = DOC(
... TITLE("The dog and the hog"),
... SECTION(
... TITLE("The dog"),
... PAR("Once upon a time, ..."),
... PAR("And then ...")
... ),
... SECTION(
... TITLE("The hog"),
... PAR("Sooner or later ...")
... )
... )
>>> print etree.tostring(my_doc, pretty_print=True),
<p:doc xmlns:p="http://my.de/fault/namespace">
<p:title>The dog and the hog</p:title>
<p:section>
<p:title>The dog</p:title>
<p:par>Once upon a time, ...</p:par>
<p:par>And then ...</p:par>
</p:section>
<p:section>
<p:title>The hog</p:title>
<p:par>Sooner or later ...</p:par>
</p:section>
</p:doc>
One such example is the module ``lxml.html.builder``, which provides a
vocabulary for HTML.
ElementPath
===========
The ElementTree library comes with a simple XPath-like path language
called ElementPath_. The main difference is that you can use the
``{namespace}tag`` notation in ElementPath expressions. However,
advanced features like value comparison and functions are not
available.
.. _ElementPath: http://effbot.org/zone/element-xpath.htm
.. _`full XPath implementation`: xpathxslt.html#xpath
In addition to a `full XPath implementation`_, lxml.etree supports the
ElementPath language in the same way ElementTree does, even using
(almost) the same implementation. The API provides four methods here
that you can find on Elements and ElementTrees:
* ``iterfind()`` iterates over all Elements that match the path
expression
* ``findall()`` returns a list of matching Elements
* ``find()`` efficiently returns only the first match
* ``findtext()`` returns the ``.text`` content of the first match
Here are some examples::
>>> root = etree.XML("<root><a x='123'>aText<b/><c/><b/></a></root>")
Find a child of an Element::
>>> print root.find("b")
None
>>> print root.find("a").tag
a
Find an Element anywhere in the tree::
>>> print root.find(".//b").tag
b
>>> [ b.tag for b in root.iterfind(".//b") ]
['b', 'b']
Find Elements with a certain attribute::
>>> print root.findall(".//a[@x]")[0].tag
a
>>> print root.findall(".//a[@y]")
[]
