Combinators and Selector Lists
CSS employs a number of tokens in order to represent lists or to provide relational context between two selectors.
Selector Lists
Selector lists use the comma (,) to join multiple selectors in a list. When presented with a selector list, any selector in the list that matches an element will return that element.
element1, element2
>>> from bs4 import BeautifulSoup as bs
>>> html = """
... <html>
... <head></head>
... <body>
... <h1>Title</h1>
... <p>Paragraph</p>
... </body>
... </html>
... """
>>> soup = bs(html, 'html5lib')
>>> print(soup.select('h1, p'))
[<h1>Title</h1>, <p>Paragraph</p>]
Descendant Combinator
Descendant combinators combine two selectors with whitespace ( ) in order to signify that the second element is matched if it has an ancestor that matches the first element.
parent descendant
>>> from bs4 import BeautifulSoup as bs
>>> html = """
... <html>
... <head></head>
... <body>
... <div><p>Paragraph 1</p></div>
... <div><p>Paragraph 2</p></div>
... </body>
... </html>
... """
>>> soup = bs(html, 'html5lib')
>>> print(soup.select('body p'))
[<p>Paragraph 1</p>, <p>Paragraph 2</p>]
Additional Reading
https://developer.mozilla.org/en-US/docs/Web/CSS/Descendant_combinator
Child combinator
Child combinators combine two selectors with > in order to signify that the second element is matched if it has a parent that matches the first element.
parent > child
>>> from bs4 import BeautifulSoup as bs
>>> html = """
... <html>
... <head></head>
... <body>
... <div><p>Paragraph 1</p></div>
... <div><ul><li><p>Paragraph 2</p></li></ul></div>
... </body>
... </html>
... """
>>> soup = bs(html, 'html5lib')
>>> print(soup.select('div > p'))
[<p>Paragraph 1</p>]
Additional Reading
https://developer.mozilla.org/en-US/docs/Web/CSS/Child_combinator
General sibling combinator
General sibling combinators combine two selectors with ~ in order to signify that the second element is matched if it has a sibling that precedes it that matches the first element.
prevsibling ~ sibling
>>> from bs4 import BeautifulSoup as bs
>>> html = """
... <html>
... <head></head>
... <body>
... <h1>Title</h1>
... <p>Paragraph 1</p>
... <p>Paragraph 2</p>
... </body>
... </html>
... """
>>> soup = bs(html, 'html5lib')
>>> print(soup.select('h1 ~ p'))
[<p>Paragraph 1</p>, <p>Paragraph 2</p>]
Additional Reading
https://developer.mozilla.org/en-US/docs/Web/CSS/General_sibling_combinator
Adjacent sibling combinator
Adjacent sibling combinators combine two selectors with + in order to signify that the second element is matched if it has an adjacent sibling that precedes it that matches the first element.
prevsibling + nextsibling
>>> from bs4 import BeautifulSoup as bs
>>> html = """
... <html>
... <head></head>
... <body>
... <h1>Title</h1>
... <p>Paragraph 1</p>
... <p>Paragraph 2</p>
... </body>
... </html>
... """
>>> soup = bs(html, 'html5lib')
>>> print(soup.select('h1 + p'))
[<p>Paragraph 1</p>]
Additional Reading
https://developer.mozilla.org/en-US/docs/Web/CSS/Adjacent_sibling_combinator