- lxml

- Developing with lxml

- Extending lxml

- Developing lxml

# html5lib Parser

html5lib is a Python package that implements the HTML5 parsing algorithm which is heavily influenced by current browsers and based on the WHATWG HTML5 specification.

lxml can benefit from the parsing capabilities of html5lib through the `lxml.html.html5parser` module. It provides a similar interface to the `lxml.html` module by providing `fromstring()`, `parse()`, `document_fromstring()`, `fragment_fromstring()` and `fragments_fromstring()` that work like the regular html parsing functions.

# Differences to regular HTML parsing

There are a few differences in the returned tree to the regular HTML parsing functions from `lxml.html`. html5lib normalizes some elements and element structures to a common format. For example even if a tables does not have a tbody html5lib will inject one automatically:

    >>> from lxml.html import tostring, html5parser
    >>> tostring(html5parser.fromstring("<table><td>foo"))
    '<table><tbody><tr><td>foo</td></tr></tbody></table>'

Also the parameters the functions accept are different.

# Function Reference

`parse(filename_url_or_file)`:
  Parses the named file or url, or if the object has a `.read()` method, parses from that.
`document_fromstring(html, guess_charset=True)`:

  Parses a document from the given string. This always creates a correct HTML document, which means the parent node is `<html>`, and there is a body and possibly a head.

  If a bytestring is passed and `guess_charset` is true the chardet library (if installed) will guess the charset if ambiguities exist.

`fragment_fromstring(string, create_parent=False, guess_charset=False)`:

  Returns an HTML fragment from a string. The fragment must contain just a single element, unless `create_parent` is given; e.g,. `fragment_fromstring(string, create_parent='div')` will wrap the element in a `<div>`. If `create_parent` is true the default parent tag (div) is used.

  If a bytestring is passed and `guess_charset` is true the chardet library (if installed) will guess the charset if ambiguities exist.

`fragments_fromstring(string, no_leading_text=False, parser=None)`:

  Returns a list of the elements found in the fragment. The first item in the list may be a string. If `no_leading_text` is true, then it will be an error if there is leading text, and it will always be a list of only elements.

  If a bytestring is passed and `guess_charset` is true the chardet library (if installed) will guess the charset if ambiguities exist.

`fromstring(string)`:
  Returns `document_fromstring` or `fragment_fromstring`, based on whether the string looks like a full document, or just a fragment.

Additionally all parsing functions accept an `parser` keyword argument that can be set to a custom parser instance. To create custom parsers you can subclass the `HTMLParser` and `XHTMLParser` from the same module. Note that these are the parser classes provided by html5lib.