lxml supports a number of interesting languages for tree traversal and element selection. The most important is obviously XPath, but there is also ObjectPath in the lxml.objectify module. The newest child of this family is CSS selection, which is made available in form of the lxml.cssselect module.

Although it started its life in lxml, cssselect is now an independent project. It translates CSS selectors to XPath 1.0 expressions that can be used with lxml's XPath engine. lxml.cssselect adds a few convenience shortcuts into that package.


The CSSSelector class

The most important class in the lxml.cssselect module is CSSSelector. It provides the same interface as the XPath class, but accepts a CSS selector expression as input:

>>> from lxml.cssselect import CSSSelector
>>> sel = CSSSelector('div.content')
>>> sel  #doctest: +ELLIPSIS
<CSSSelector ... for 'div.content'>
>>> sel.css

The selector actually compiles to XPath, and you can see the expression by inspecting the object:

>>> sel.path
"descendant-or-self::div[@class and contains(concat(' ', normalize-space(@class), ' '), ' content ')]"

To use the selector, simply call it with a document or element object:

>>> from lxml.etree import fromstring
>>> h = fromstring('''<div id="outer">
...   <div id="inner" class="content body">
...       text
...   </div></div>''')
>>> [e.get('id') for e in sel(h)]

Using CSSSelector is equivalent to translating with cssselect and using the XPath class:

>>> from cssselect import GenericTranslator
>>> from lxml.etree import XPath
>>> sel = XPath(GenericTranslator().css_to_xpath('div.content'))

CSSSelector takes a translator parameter to let you choose which translator to use. It can be 'xml' (the default), 'xhtml', 'html' or a Translator object.

The cssselect method

lxml Element objects have a cssselect convenience method.

>>> h.cssselect('div.content') == sel(h)

Note however that pre-compiling the expression with the CSSSelector or XPath class can provide a substantial speedup.

The method also accepts a translator parameter. On HtmlElement objects, the default is changed to 'html'.

Supported Selectors

Most Level 3 selectors are supported. The details are in the cssselect documentation.


In CSS you can use namespace-prefix|element, similar to namespace-prefix:element in an XPath expression. In fact, it maps one-to-one, and the same rules are used to map namespace prefixes to namespace URIs: the CSSSelector class accepts a dictionary as its namespaces argument.