Usage

Create a Selector object for your input text.

For HTML or XML, use CSS or XPath expressions to select data:

>>> from parsel import Selector
>>> html_text = "<html><body><h1>Hello, Parsel!</h1></body></html>"
>>> html_selector = Selector(text=html_text)
>>> html_selector.css('h1')
[<Selector query='descendant-or-self::h1' data='<h1>Hello, Parsel!</h1>'>]
>>> html_selector.xpath('//h1')  # the same, but now with XPath
[<Selector query='//h1' data='<h1>Hello, Parsel!</h1>'>]

For JSON, use JMESPath expressions to select data:

>>> json_text = '{"title":"Hello, Parsel!"}'
>>> json_selector = Selector(text=json_text)
>>> json_selector.jmespath('title')
[<Selector query='title' data='Hello, Parsel!'>]

And extract data from those elements:

>>> html_selector.xpath('//h1/text()').get()
'Hello, Parsel!'
>>> json_selector.jmespath('title').getall()
['Hello, Parsel!']

Learning expression languages

CSS is a language for applying styles to HTML documents. It defines selectors to associate those styles with specific HTML elements. Resources to learn CSS selectors include:

Parsel support for CSS selectors comes from cssselect, so read about CSS selectors supported by cssselect.

XPath is a language for selecting nodes in XML documents, which can also be used with HTML. Resources to learn XPath include:

For HTML and XML input, you can use either CSS or XPath. CSS is usually more readable, but some things can only be done with XPath.

JMESPath allows you to declaratively specify how to extract elements from a JSON document. Resources to learn JMESPath include:

Using selectors

To explain how to use the selectors we’ll use the requests library to download an example page located in the Parsel’s documentation:

For the sake of completeness, here’s its full HTML code:

<html>
 <head>
  <base href='http://example.com/' />
  <title>Example website</title>
 </head>
 <body>
  <div id='images'>
   <a href='image1.html'>Name: My image 1 <br /><img src='image1_thumb.jpg' /></a>
   <a href='image2.html'>Name: My image 2 <br /><img src='image2_thumb.jpg' /></a>
   <a href='image3.html'>Name: My image 3 <br /><img src='image3_thumb.jpg' /></a>
   <a href='image4.html'>Name: My image 4 <br /><img src='image4_thumb.jpg' /></a>
   <a href='image5.html'>Name: My image 5 <br /><img src='image5_thumb.jpg' /></a>
  </div>
 </body>
</html>

So, let’s download that page and create a selector for it:

>>> import requests
>>> from parsel import Selector
>>> url = 'https://parsel.readthedocs.org/en/latest/_static/selectors-sample1.html'
>>> text = requests.get(url).text
>>> selector = Selector(text=text)

Since we’re dealing with HTML, the default type for Selector, we don’t need to specify the type argument.

So, by looking at the HTML code of that page, let’s construct an XPath for selecting the text inside the title tag:

>>> selector.xpath('//title/text()')
[<Selector query='//title/text()' data='Example website'>]

You can also ask the same thing using CSS instead:

>>> selector.css('title::text')
[<Selector query='descendant-or-self::title/text()' data='Example website'>]

To actually extract the textual data, you must call the selector .get() or .getall() methods, as follows:

>>> selector.xpath('//title/text()').getall()
['Example website']
>>> selector.xpath('//title/text()').get()
'Example website'

.get() always returns a single result; if there are several matches, content of a first match is returned; if there are no matches, None is returned. .getall() returns a list with all results.

Notice that CSS selectors can select text or attribute nodes using CSS3 pseudo-elements:

>>> selector.css('title::text').get()
'Example website'

As you can see, .xpath() and .css() methods return a SelectorList instance, which is a list of new selectors. This API can be used for quickly selecting nested data:

>>> selector.css('img').xpath('@src').getall()
['image1_thumb.jpg',
 'image2_thumb.jpg',
 'image3_thumb.jpg',
 'image4_thumb.jpg',
 'image5_thumb.jpg']

If you want to extract only the first matched element, you can call the selector .get() (or its alias .extract_first() commonly used in previous parsel versions):

>>> selector.xpath('//div[@id="images"]/a/text()').get()
'Name: My image 1 '

It returns None if no element was found:

>>> selector.xpath('//div[@id="not-exists"]/text()').get() is None
True

Instead of using e.g. '@src' XPath it is possible to query for attributes using .attrib property of a Selector:

>>> [img.attrib['src'] for img in selector.css('img')]
['image1_thumb.jpg',
 'image2_thumb.jpg',
 'image3_thumb.jpg',
 'image4_thumb.jpg',
 'image5_thumb.jpg']

As a shortcut, .attrib is also available on SelectorList directly; it returns attributes for the first matching element:

>>> selector.css('img').attrib['src']
'image1_thumb.jpg'

This is most useful when only a single result is expected, e.g. when selecting by id, or selecting unique elements on a web page:

>>> selector.css('base').attrib['href']
'http://example.com/'

Now we’re going to get the base URL and some image links:

>>> selector.xpath('//base/@href').get()
'http://example.com/'

>>> selector.css('base::attr(href)').get()
'http://example.com/'

>>> selector.css('base').attrib['href']
'http://example.com/'

>>> selector.xpath('//a[contains(@href, "image")]/@href').getall()
['image1.html',
 'image2.html',
 'image3.html',
 'image4.html',
 'image5.html']

>>> selector.css('a[href*=image]::attr(href)').getall()
['image1.html',
 'image2.html',
 'image3.html',
 'image4.html',
 'image5.html']

>>> selector.xpath('//a[contains(@href, "image")]/img/@src').getall()
['image1_thumb.jpg',
 'image2_thumb.jpg',
 'image3_thumb.jpg',
 'image4_thumb.jpg',
 'image5_thumb.jpg']

>>> selector.css('a[href*=image] img::attr(src)').getall()
['image1_thumb.jpg',
 'image2_thumb.jpg',
 'image3_thumb.jpg',
 'image4_thumb.jpg',
 'image5_thumb.jpg']

Extensions to CSS Selectors

Per W3C standards, CSS selectors do not support selecting text nodes or attribute values. But selecting these is so essential in a web scraping context that Parsel implements a couple of non-standard pseudo-elements:

  • to select text nodes, use ::text

  • to select attribute values, use ::attr(name) where name is the name of the attribute that you want the value of

Warning

These pseudo-elements are Scrapy-/Parsel-specific. They will most probably not work with other libraries like lxml or PyQuery.

Examples:

  • title::text selects children text nodes of a descendant <title> element:

    >>> selector.css('title::text').get()
'Example website'

  • *::text selects all descendant text nodes of the current selector context:

    >>> selector.css('#images *::text').getall()
['\n   ',
 'Name: My image 1 ',
 '\n   ',
 'Name: My image 2 ',
 '\n   ',
 'Name: My image 3 ',
 '\n   ',
 'Name: My image 4 ',
 '\n   ',
 'Name: My image 5 ',
 '\n  ']

  • a::attr(href) selects the href attribute value of descendant links:

    >>> selector.css('a::attr(href)').getall()
['image1.html',
 'image2.html',
 'image3.html',
 'image4.html',
 'image5.html']

Note

You cannot chain these pseudo-elements. But in practice it would not make much sense: text nodes do not have attributes, and attribute values are string values already and do not have children nodes.

Note

See also: Selecting element attributes.

Nesting selectors

The selection methods (.xpath() or .css()) return a list of selectors of the same type, so you can call the selection methods for those selectors too. Here’s an example:

>>> links = selector.xpath('//a[contains(@href, "image")]')
>>> links.getall()
['<a href="image1.html">Name: My image 1 <br><img src="image1_thumb.jpg"></a>',
 '<a href="image2.html">Name: My image 2 <br><img src="image2_thumb.jpg"></a>',
 '<a href="image3.html">Name: My image 3 <br><img src="image3_thumb.jpg"></a>',
 '<a href="image4.html">Name: My image 4 <br><img src="image4_thumb.jpg"></a>',
 '<a href="image5.html">Name: My image 5 <br><img src="image5_thumb.jpg"></a>']

>>> for index, link in enumerate(links):
...     args = (index, link.xpath('@href').get(), link.xpath('img/@src').get())
...     print('Link number %d points to url %r and image %r' % args)
Link number 0 points to url 'image1.html' and image 'image1_thumb.jpg'
Link number 1 points to url 'image2.html' and image 'image2_thumb.jpg'
Link number 2 points to url 'image3.html' and image 'image3_thumb.jpg'
Link number 3 points to url 'image4.html' and image 'image4_thumb.jpg'
Link number 4 points to url 'image5.html' and image 'image5_thumb.jpg'

Selecting element attributes

There are several ways to get a value of an attribute. First, one can use XPath syntax:

>>> selector.xpath("//a/@href").getall()
['image1.html', 'image2.html', 'image3.html', 'image4.html', 'image5.html']

XPath syntax has a few advantages: it is a standard XPath feature, and @attributes can be used in other parts of an XPath expression - e.g. it is possible to filter by attribute value.

parsel also provides an extension to CSS selectors (::attr(...)) which allows to get attribute values:

>>> selector.css('a::attr(href)').getall()
['image1.html', 'image2.html', 'image3.html', 'image4.html', 'image5.html']

In addition to that, there is a .attrib property of Selector. You can use it if you prefer to lookup attributes in Python code, without using XPaths or CSS extensions:

>>> [a.attrib['href'] for a in selector.css('a')]
['image1.html', 'image2.html', 'image3.html', 'image4.html', 'image5.html']

This property is also available on SelectorList; it returns a dictionary with attributes of a first matching element. It is convenient to use when a selector is expected to give a single result (e.g. when selecting by element ID, or when selecting an unique element on a page):

>>> selector.css('base').attrib
{'href': 'http://example.com/'}
>>> selector.css('base').attrib['href']
'http://example.com/'

.attrib property of an empty SelectorList is empty:

>>> selector.css('foo').attrib
{}

Using selectors with regular expressions

Selector also has a .re() method for extracting data using regular expressions. However, unlike using .xpath() or .css() methods, .re() returns a list of strings. So you can’t construct nested .re() calls.

Here’s an example used to extract image names from the HTML code above:

>>> selector.xpath('//a[contains(@href, "image")]/text()').re(r'Name:\s*(.*)')
['My image 1 ',
 'My image 2 ',
 'My image 3 ',
 'My image 4 ',
 'My image 5 ']

There’s an additional helper reciprocating .get() (and its alias .extract_first()) for .re(), named .re_first(). Use it to extract just the first matching string:

>>> selector.xpath('//a[contains(@href, "image")]/text()').re_first(r'Name:\s*(.*)')
'My image 1 '

Working with relative XPaths

Keep in mind that if you are nesting selectors and use an XPath that starts with /, that XPath will be absolute to the document and not relative to the selector you’re calling it from.

For example, suppose you want to extract all <p> elements inside <div> elements. First, you would get all <div> elements:

>>> divs = selector.xpath('//div')

At first, you may be tempted to use the following approach, which is wrong, as it actually extracts all <p> elements from the document, not only those inside <div> elements:

>>> for p in divs.xpath('//p'):  # this is wrong - gets all <p> from the whole document
...     print(p.get())

This is the proper way to do it (note the dot prefixing the .//p XPath):

>>> for p in divs.xpath('.//p'):  # extracts all <p> inside
...     print(p.get())

Another common case would be to extract all direct <p> children:

>>> for p in divs.xpath('p'):
...     print(p.get())

For more details about relative XPaths see the Location Paths section in the XPath specification.

Removing elements

If for any reason you need to remove elements based on a Selector or a SelectorList, you can do it with the drop() method, available for both classes.

Warning

this is a destructive action and cannot be undone. The original content of the selector is removed from the elements tree. This could be useful when trying to reduce the memory footprint of Responses.

Example removing an ad from a blog post:

>>> from parsel import Selector
>>> doc = """
... <article>
...     <div class="row">Content paragraph...</div>
...     <div class="row">
...         <div class="ad">
...             Ad content...
...             <a href="http://...">Link</a>
...         </div>
...     </div>
...     <div class="row">More content...</div>
... </article>
... """
>>> sel = Selector(text=doc)
>>> sel.xpath('//div/text()').getall()
['Content paragraph...', '\n        ', '\n            Ad content...\n            ', '\n        ', '\n    ', 'More content...']
>>> sel.xpath('//div[@class="ad"]').drop()
>>> sel.xpath('//div//text()').getall()
['Content paragraph...', 'More content...']

Using EXSLT extensions

Being built atop lxml, parsel selectors support some EXSLT extensions and come with these pre-registered namespaces to use in XPath expressions:

prefix

namespace

usage

re

http://exslt.org/regular-expressions

regular expressions

set

http://exslt.org/sets

set manipulation

Regular expressions

The test() function, for example, can prove quite useful when XPath’s starts-with() or contains() are not sufficient.

Example selecting links in list item with a “class” attribute ending with a digit:

>>> from parsel import Selector
>>> doc = """
... <div>
...     <ul>
...         <li class="item-0"><a href="link1.html">first item</a></li>
...         <li class="item-1"><a href="link2.html">second item</a></li>
...         <li class="item-inactive"><a href="link3.html">third item</a></li>
...         <li class="item-1"><a href="link4.html">fourth item</a></li>
...         <li class="item-0"><a href="link5.html">fifth item</a></li>
...     </ul>
... </div>
... """
>>> sel = Selector(text=doc)
>>> sel.xpath('//li//@href').getall()
['link1.html', 'link2.html', 'link3.html', 'link4.html', 'link5.html']
>>> sel.xpath(r'//li[re:test(@class, "item-\d$")]//@href').getall()
['link1.html', 'link2.html', 'link4.html', 'link5.html']
>>>

Warning

C library libxslt doesn’t natively support EXSLT regular expressions so lxml’s implementation uses hooks to Python’s re module. Thus, using regexp functions in your XPath expressions may add a small performance penalty.

Set operations

These can be handy for excluding parts of a document tree before extracting text elements for example.

Example extracting microdata (sample content taken from http://schema.org/Product) with groups of itemscopes and corresponding itemprops:

>>> doc = """
... <div itemscope itemtype="http://schema.org/Product">
...   <span itemprop="name">Kenmore White 17" Microwave</span>
...   <img src="kenmore-microwave-17in.jpg" alt='Kenmore 17" Microwave' />
...   <div itemprop="aggregateRating"
...     itemscope itemtype="http://schema.org/AggregateRating">
...    Rated <span itemprop="ratingValue">3.5</span>/5
...    based on <span itemprop="reviewCount">11</span> customer reviews
...   </div>
...
...   <div itemprop="offers" itemscope itemtype="http://schema.org/Offer">
...     <span itemprop="price">$55.00</span>
...     <link itemprop="availability" href="http://schema.org/InStock" />In stock
...   </div>
...
...   Product description:
...   <span itemprop="description">0.7 cubic feet countertop microwave.
...   Has six preset cooking categories and convenience features like
...   Add-A-Minute and Child Lock.</span>
...
...   Customer reviews:
...
...   <div itemprop="review" itemscope itemtype="http://schema.org/Review">
...     <span itemprop="name">Not a happy camper</span> -
...     by <span itemprop="author">Ellie</span>,
...     <meta itemprop="datePublished" content="2011-04-01">April 1, 2011
...     <div itemprop="reviewRating" itemscope itemtype="http://schema.org/Rating">
...       <meta itemprop="worstRating" content = "1">
...       <span itemprop="ratingValue">1</span>/
...       <span itemprop="bestRating">5</span>stars
...     </div>
...     <span itemprop="description">The lamp burned out and now I have to replace
...     it. </span>
...   </div>
...
...   <div itemprop="review" itemscope itemtype="http://schema.org/Review">
...     <span itemprop="name">Value purchase</span> -
...     by <span itemprop="author">Lucas</span>,
...     <meta itemprop="datePublished" content="2011-03-25">March 25, 2011
...     <div itemprop="reviewRating" itemscope itemtype="http://schema.org/Rating">
...       <meta itemprop="worstRating" content = "1"/>
...       <span itemprop="ratingValue">4</span>/
...       <span itemprop="bestRating">5</span>stars
...     </div>
...     <span itemprop="description">Great microwave for the price. It is small and
...     fits in my apartment.</span>
...   </div>
...   ...
... </div>
... """
>>> sel = Selector(text=doc, type="html")
>>> for scope in sel.xpath('//div[@itemscope]'):
...     print("current scope:", scope.xpath('@itemtype').getall())
...     props = scope.xpath('''
...                 set:difference(./descendant::*/@itemprop,
...                                .//*[@itemscope]/*/@itemprop)''')
...     print("    properties: %s" % (props.getall()))
...     print("")
current scope: ['http://schema.org/Product']
    properties: ['name', 'aggregateRating', 'offers', 'description', 'review', 'review']

current scope: ['http://schema.org/AggregateRating']
    properties: ['ratingValue', 'reviewCount']

current scope: ['http://schema.org/Offer']
    properties: ['price', 'availability']

current scope: ['http://schema.org/Review']
    properties: ['name', 'author', 'datePublished', 'reviewRating', 'description']

current scope: ['http://schema.org/Rating']
    properties: ['worstRating', 'ratingValue', 'bestRating']

current scope: ['http://schema.org/Review']
    properties: ['name', 'author', 'datePublished', 'reviewRating', 'description']

current scope: ['http://schema.org/Rating']
    properties: ['worstRating', 'ratingValue', 'bestRating']

Here we first iterate over itemscope elements, and for each one, we look for all itemprops elements and exclude those that are themselves inside another itemscope.

Other XPath extensions

Parsel also defines a sorely missed XPath extension function has-class that returns True for nodes that have all of the specified HTML classes:

>>> from parsel import Selector
>>> sel = Selector("""
...         <p class="foo bar-baz">First</p>
...         <p class="foo">Second</p>
...         <p class="bar">Third</p>
...         <p>Fourth</p>
... """)
...
>>> sel.xpath('//p[has-class("foo")]')
[<Selector query='//p[has-class("foo")]' data='<p class="foo bar-baz">First</p>'>,
 <Selector query='//p[has-class("foo")]' data='<p class="foo">Second</p>'>]
>>> sel.xpath('//p[has-class("foo", "bar-baz")]')
[<Selector query='//p[has-class("foo", "bar-baz")]' data='<p class="foo bar-baz">First</p>'>]
>>> sel.xpath('//p[has-class("foo", "bar")]')
[]

So XPath //p[has-class("foo", "bar-baz")] is roughly equivalent to CSS p.foo.bar-baz. Please note, that it is slower in most of the cases, because it’s a pure-Python function that’s invoked for every node in question whereas the CSS lookup is translated into XPath and thus runs more efficiently, so performance-wise its uses are limited to situations that are not easily described with CSS selectors.

Parsel also simplifies adding your own XPath extensions.

parsel.xpathfuncs.set_xpathfunc(fname: str, func: Callable | None) → None[source]

Register a custom extension function to use in XPath expressions.

The function func registered under fname identifier will be called for every matching node, being passed a context parameter as well as any parameters passed from the corresponding XPath expression.

If func is None, the extension function will be removed.

See more in lxml documentation.

Some XPath tips

Here are some tips that you may find useful when using XPath with Parsel, based on this post from Zyte’s blog. If you are not much familiar with XPath yet, you may want to take a look first at this XPath tutorial.

Using text nodes in a condition

When you need to use the text content as argument to an XPath string function, avoid using .//text() and use just . instead.

This is because the expression .//text() yields a collection of text elements – a node-set. And when a node-set is converted to a string, which happens when it is passed as argument to a string function like contains() or starts-with(), it results in the text for the first element only.

Example:

>>> from parsel import Selector
>>> sel = Selector(text='<a href="#">Click here to go to the <strong>Next Page</strong></a>')

Converting a node-set to string:

>>> sel.xpath('//a//text()').getall() # take a peek at the node-set
['Click here to go to the ', 'Next Page']
>>> sel.xpath("string(//a[1]//text())").getall() # convert it to string
['Click here to go to the ']

A node converted to a string, however, puts together the text of itself plus of all its descendants:

>>> sel.xpath("//a[1]").getall() # select the first node
['<a href="#">Click here to go to the <strong>Next Page</strong></a>']
>>> sel.xpath("string(//a[1])").getall() # convert it to string
['Click here to go to the Next Page']

So, using the .//text() node-set won’t select anything in this case:

>>> sel.xpath("//a[contains(.//text(), 'Next Page')]").getall()
[]

But using the . to mean the node, works:

>>> sel.xpath("//a[contains(., 'Next Page')]").getall()
['<a href="#">Click here to go to the <strong>Next Page</strong></a>']

Beware of the difference between //node[1] and (//node)[1]

//node[1] selects all the nodes occurring first under their respective parents.

(//node)[1] selects all the nodes in the document, and then gets only the first of them.

Example:

>>> from parsel import Selector
>>> sel = Selector(text="""
...     <ul class="list">
...         <li>1</li>
...         <li>2</li>
...         <li>3</li>
...     </ul>
...     <ul class="list">
...         <li>4</li>
...         <li>5</li>
...         <li>6</li>
...     </ul>""")
>>> xp = lambda x: sel.xpath(x).getall()

This gets all first <li> elements under whatever it is its parent:

>>> xp("//li[1]")
['<li>1</li>', '<li>4</li>']

And this gets the first <li> element in the whole document:

>>> xp("(//li)[1]")
['<li>1</li>']

This gets all first <li> elements under an <ul> parent:

>>> xp("//ul/li[1]")
['<li>1</li>', '<li>4</li>']

And this gets the first <li> element under an <ul> parent in the whole document:

>>> xp("(//ul/li)[1]")
['<li>1</li>']

When querying by class, consider using CSS

Because an element can contain multiple CSS classes, the XPath way to select elements by class is the rather verbose:

*[contains(concat(' ', normalize-space(@class), ' '), ' someclass ')]

If you use @class='someclass' you may end up missing elements that have other classes, and if you just use contains(@class, 'someclass') to make up for that you may end up with more elements that you want, if they have a different class name that shares the string someclass.

As it turns out, parsel selectors allow you to chain selectors, so most of the time you can just select by class using CSS and then switch to XPath when needed:

>>> from parsel import Selector
>>> sel = Selector(text='<div class="hero shout"><time datetime="2014-07-23 19:00">Special date</time></div>')
>>> sel.css('.shout').xpath('./time/@datetime').getall()
['2014-07-23 19:00']

This is cleaner than using the verbose XPath trick shown above. Just remember to use the . in the XPath expressions that will follow.

Beware of how script and style tags differ from other tags

Following the standard, the contents of script and style elements are parsed as plain text.

This means that XML-like structures found within them, including comments, are all treated as part of the element text, and not as separate nodes.

For example:

>>> from parsel import Selector
>>> selector = Selector(text="""
...     <script>
...         text
...         <!-- comment -->
...         <br/>
...     </script>
...     <style>
...         text
...         <!-- comment -->
...         <br/>
...     </style>
...     <div>
...         text
...         <!-- comment -->
...         <br/>
...     </div>""")
>>> for tag in selector.xpath('//*[contains(text(), "text")]'):
...     print(tag.xpath('name()').get())
...     print('    Text: ' + (tag.xpath('text()').get() or ''))
...     print('    Comment: ' + (tag.xpath('comment()').get() or ''))
...     print('    Children: ' + ''.join(tag.xpath('*').getall()))
...
script
    Text:
        text
        <!-- comment -->
        <br/>

    Comment:
    Children:
style
    Text:
        text
        <!-- comment -->
        <br/>

    Comment:
    Children:
div
    Text:
        text

    Comment: <!-- comment -->
    Children: <br>

extract() and extract_first()

If you’re a long-time parsel (or Scrapy) user, you’re probably familiar with .extract() and .extract_first() selector methods. These methods are still supported by parsel, there are no plans to deprecate them.

However, parsel usage docs are now written using .get() and .getall() methods. We feel that these new methods result in more concise and readable code.

The following examples show how these methods map to each other.

  1. SelectorList.get() is the same as SelectorList.extract_first():

    >>> selector.css('a::attr(href)').get()
'image1.html'
>>> selector.css('a::attr(href)').extract_first()
'image1.html'

  2. SelectorList.getall() is the same as SelectorList.extract():

    >>> selector.css('a::attr(href)').getall()
['image1.html', 'image2.html', 'image3.html', 'image4.html', 'image5.html']
>>> selector.css('a::attr(href)').extract()
['image1.html', 'image2.html', 'image3.html', 'image4.html', 'image5.html']

  3. Selector.get() is the same as Selector.extract():

    >>> selector.css('a::attr(href)')[0].get()
'image1.html'
>>> selector.css('a::attr(href)')[0].extract()
'image1.html'

  4. For consistency, there is also Selector.getall(), which returns a list:

    >>> selector.css('a::attr(href)')[0].getall()
['image1.html']

With the .extract() method it was not always obvious if a result is a list or not; to get a single result either .extract() or .extract_first() needed to be called, depending whether you had a Selector or SelectorList.

So, the main difference is that the outputs of .get() and .getall() are more predictable: .get() always returns a single result, .getall() always returns a list of all extracted results.

Using CSS selectors in multi-root documents

Some webpages may have multiple root elements. It can happen, for example, when a webpage has broken code, such as missing closing tags.

You can use XPath to determine if a page has multiple root elements:

>>> len(selector.xpath('/*')) > 1
True

CSS selectors only work on the first root element, because the first root element is always used as the starting current element, and CSS selectors do not allow selecting parent elements (XPath’s ..) or elements relative to the document root (XPath’s /).

If you want to use a CSS selector that takes into account all root elements, you need to precede your CSS query by an XPath query that reaches all root elements:

selector.xpath('/*').css('<your CSS selector>')

Command-Line Interface Tools

There are third-party tools that allow using Parsel from the command line:

  • Parsel CLI allows applying Parsel selectors to the standard input. For example, you can apply a Parsel selector to the output of cURL.

  • parselcli provides an interactive shell that allows applying Parsel selectors to a remote URL or a local file.

Examples

Working on HTML

Here are some Selector examples to illustrate several concepts. In all cases, we assume there is already a Selector instantiated with an HTML text like this:

sel = Selector(text=html_text)

  1. Select all <h1> elements from an HTML text, returning a list of Selector objects (ie. a SelectorList object):

    sel.xpath("//h1")

  2. Extract the text of all <h1> elements from an HTML text, returning a list of strings:

    sel.xpath("//h1").getall()         # this includes the h1 tag
sel.xpath("//h1/text()").getall()  # this excludes the h1 tag

  3. Iterate over all <p> tags and print their class attribute:

    for node in sel.xpath("//p"):
    print(node.attrib['class'])

Working on XML (and namespaces)

Here are some examples to illustrate concepts for Selector objects instantiated with an XML text like this:

sel = Selector(text=xml_text, type='xml')

  1. Select all <product> elements from an XML text, returning a list of Selector objects (ie. a SelectorList object):

    sel.xpath("//product")

  2. Extract all prices from a Google Base XML feed which requires registering a namespace:

    sel.register_namespace("g", "http://base.google.com/ns/1.0")
sel.xpath("//g:price").getall()

Removing namespaces

When dealing with scraping projects, it is often quite convenient to get rid of namespaces altogether and just work with element names, to write more simple/convenient XPaths. You can use the Selector.remove_namespaces method for that.

Let’s show an example that illustrates this with the Python Insider blog atom feed.

Let’s download the atom feed using requests and create a selector:

>>> import requests
>>> from parsel import Selector
>>> text = requests.get('https://feeds.feedburner.com/PythonInsider').text
>>> sel = Selector(text=text, type='xml')

This is how the file starts:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet ... ?>
<feed xmlns="http://www.w3.org/2005/Atom"
      xmlns:openSearch="http://a9.com/-/spec/opensearchrss/1.0/"
      xmlns:blogger="http://schemas.google.com/blogger/2008"
      xmlns:georss="http://www.georss.org/georss"
      xmlns:gd="http://schemas.google.com/g/2005"
      xmlns:thr="http://purl.org/syndication/thread/1.0"
      xmlns:feedburner="http://rssnamespace.org/feedburner/ext/1.0">
  ...
</feed>

You can see several namespace declarations including a default “http://www.w3.org/2005/Atom” and another one using the “gd:” prefix for “http://schemas.google.com/g/2005”.

We can try selecting all <link> objects and then see that it doesn’t work (because the Atom XML namespace is obfuscating those nodes):

>>> sel.xpath("//link")
[]

But once we call the Selector.remove_namespaces method, all nodes can be accessed directly by their names:

>>> sel.remove_namespaces()
>>> sel.xpath("//link")
[<Selector query='//link' data='<link rel="alternate" type="text/html...'>,
 <Selector query='//link' data='<link rel="next" type="application/at...'>,
 ...]

If you wonder why the namespace removal procedure isn’t called always by default instead of having to call it manually, this is because of two reasons, which, in order of relevance, are:

  1. Removing namespaces requires to iterate and modify all nodes in the document, which is a reasonably expensive operation to perform by default for all documents.

  2. There could be some cases where using namespaces is actually required, in case some element names clash between namespaces. These cases are very rare though.

Ad-hoc namespaces references

Selector objects also allow passing namespaces references along with the query, through a namespaces argument, with the prefixes you declare being used in your XPath or CSS query.

Let’s use the same Python Insider Atom feed:

>>> import requests
>>> from parsel import Selector
>>> text = requests.get('https://feeds.feedburner.com/PythonInsider').text
>>> sel = Selector(text=text, type='xml')

And try to select the links again, now using an “atom:” prefix for the “link” node test:

>>> sel.xpath("//atom:link", namespaces={"atom": "http://www.w3.org/2005/Atom"})
[<Selector query='//atom:link' data='<link xmlns="http://www.w3.org/2005/A...'>,
 <Selector query='//atom:link' data='<link xmlns="http://www.w3.org/2005/A...'>,
 ...]

You can pass several namespaces (here we’re using shorter 1-letter prefixes):

>>> sel.xpath("//a:entry/a:author/g:image/@src",
...           namespaces={"a": "http://www.w3.org/2005/Atom",
...                       "g": "http://schemas.google.com/g/2005"}).getall()
['https://img1.blogblog.com/img/b16-rounded.gif',
 'https://img1.blogblog.com/img/b16-rounded.gif',
 ...]

Variables in XPath expressions

XPath allows you to reference variables in your XPath expressions, using the $somevariable syntax. This is somewhat similar to parameterized queries or prepared statements in the SQL world where you replace some arguments in your queries with placeholders like ?, which are then substituted with values passed with the query.

Here’s an example to match an element based on its normalized string-value:

>>> str_to_match = "Name: My image 3"
>>> selector.xpath('//a[normalize-space(.)=$match]',
...                match=str_to_match).get()
'<a href="image3.html">Name: My image 3 <br><img src="image3_thumb.jpg"></a>'

All variable references must have a binding value when calling .xpath() (otherwise you’ll get a ValueError: XPath error: exception). This is done by passing as many named arguments as necessary.

Here’s another example using a position range passed as two integers:

>>> start, stop = 2, 4
>>> selector.xpath('//a[position()>=$_from and position()<=$_to]',
...                _from=start, _to=stop).getall()
['<a href="image2.html">Name: My image 2 <br><img src="image2_thumb.jpg"></a>',
 '<a href="image3.html">Name: My image 3 <br><img src="image3_thumb.jpg"></a>',
 '<a href="image4.html">Name: My image 4 <br><img src="image4_thumb.jpg"></a>']

Named variables can be useful when strings need to be escaped for single or double quotes characters. The example below would be a bit tricky to get right (or legible) without a variable reference:

>>> html = '''<html>
... <body>
...   <p>He said: "I don't know why, but I like mixing single and double quotes!"</p>
... </body>
... </html>'''
>>> selector = Selector(text=html)
>>>
>>> selector.xpath('//p[contains(., $mystring)]',
...                mystring='''He said: "I don't know''').get()
'<p>He said: "I don\'t know why, but I like mixing single and double quotes!"</p>'

Converting CSS to XPath

parsel.css2xpath(query: str) → str[source]

Return translated XPath version of a given CSS query

When you’re using an API that only accepts XPath expressions, it’s sometimes useful to convert CSS to XPath. This allows you to take advantage of the conciseness of CSS to query elements by classes and the easeness of manipulating XPath expressions at the same time.

On those occasions, use the function css2xpath():

>>> from parsel import css2xpath
>>> css2xpath('h1.title')
"descendant-or-self::h1[@class and contains(concat(' ', normalize-space(@class), ' '), ' title ')]"
>>> css2xpath('.profile-data') + '//h2'
"descendant-or-self::*[@class and contains(concat(' ', normalize-space(@class), ' '), ' profile-data ')]//h2"

As you can see from the examples above, it returns the translated CSS query into an XPath expression as a string, which you can use as-is or combine to build a more complex expression, before feeding to a function expecting XPath.

Similar libraries

  • BeautifulSoup is a very popular screen scraping library among Python programmers which constructs a Python object based on the structure of the HTML code and also deals with bad markup reasonably well.

  • lxml is an XML parsing library (which also parses HTML) with a pythonic API based on ElementTree. (lxml is not part of the Python standard library.). Parsel uses it under-the-hood.

  • PyQuery is a library that, like Parsel, uses lxml and cssselect under the hood, but it offers a jQuery-like API to traverse and manipulate XML/HTML documents.

Parsel is built on top of the lxml library, which means they’re very similar in speed and parsing accuracy. The advantage of using Parsel over lxml is that Parsel is simpler to use and extend, unlike the lxml API which is much bigger because the lxml library can be used for many other tasks, besides selecting markup documents.