BeautifulSoup Parser

BeautifulSoup is a Python package that parses broken HTML. While libxml2 (and thus lxml) can also parse broken HTML, BeautifulSoup is a bit more forgiving and has superiour support for encoding detection.

lxml can benefit from the parsing capabilities of BeautifulSoup through the lxml.html.soupparser module. It provides three main functions: fromstring() and parse() to parse a string or file using BeautifulSoup, and convert_tree() to convert an existing BeautifulSoup tree into a list of top-level Elements.

Parsing with the soupparser

The functions fromstring() and parse() behave as known from ElementTree. The first returns a root Element, the latter returns an ElementTree.

There is also a legacy module called lxml.html.ElementSoup, which mimics the interface provided by ElementTree's own ElementSoup module. Note that the soupparser module was added in lxml 2.0.3. Previous versions of lxml 2.0.x only have the ElementSoup module.

Here is a document full of tag soup, similar to, but not quite like, HTML:

>>> tag_soup = '<meta><head><title>Hello</head<body onload=crash()>Hi all<p>'

all you need to do is pass it to the fromstring() function:

>>> from lxml.html.soupparser import fromstring
>>> root = fromstring(tag_soup)

To see what we have here, you can serialise it:

>>> from lxml.etree import tostring
>>> print tostring(root, pretty_print=True),
  <body onload="crash()">Hi all<p/></body>

Not quite what you'd expect from an HTML page, but, well, it was broken already, right? BeautifulSoup did its best, and so now it's a tree.

To control which Element implementation is used, you can pass a makeelement factory function to parse() and fromstring(). By default, this is based on the HTML parser defined in lxml.html.

Entity handling

By default, the BeautifulSoup parser also replaces the entities it finds by their character equivalent.

>>> tag_soup = '<body>&copy;&euro;&#45;&#245;&#445;<p>'
>>> body = fromstring(tag_soup).find('.//body')
>>> body.text

If you want them back on the way out, you can just serialise with the default encoding, which is 'US-ASCII'.

>>> tostring(body)

>>> tostring(body, method="html")

Any other encoding will output the respective byte sequences.

>>> tostring(body, encoding="utf-8")

>>> tostring(body, method="html", encoding="utf-8")

>>> tostring(body, encoding=unicode)

>>> tostring(body, method="html", encoding=unicode)

Using soupparser as a fallback

The downside of using this parser is that it is much slower than the HTML parser of lxml. So if performance matters, you might want to consider using soupparser only as a fallback for certain cases.

One common problem of lxml's parser is that it might not get the encoding right in cases where the document contains a <meta> tag at the wrong place. In this case, you can exploit the fact that lxml serialises much faster than most other HTML libraries for Python. Just serialise the document to unicode and if that gives you an exception, re-parse it with BeautifulSoup to see if that works better.

>>> tag_soup = '''\
... <meta http-equiv="Content-Type"
...       content="text/html;charset=utf-8" />
... <html>
...   <head>
...     <title>Hello W\xc3\xb6rld!</title>
...   </head>
...   <body>Hi all</body>
... </html>'''

>>> import lxml.html
>>> import lxml.html.soupparser

>>> root = lxml.html.fromstring(tag_soup)
>>> try:
...     ignore = tostring(root, encoding=unicode)
... except UnicodeDecodeError:
...     root = lxml.html.soupparser.fromstring(tag_soup)