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
'div.content'

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)]
['inner']

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)
True

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.

Namespaces

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.