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Standards-compliant library for parsing and serializing HTML documents and fragments in Python
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html5lib Improve the 'Coercing non-XML name' warning (#418) Apr 26, 2019
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html5lib is a pure-python library for parsing HTML. It is designed to conform to the WHATWG HTML specification, as is implemented by all major web browsers.


Simple usage follows this pattern:

import html5lib
with open("mydocument.html", "rb") as f:
    document = html5lib.parse(f)


import html5lib
document = html5lib.parse("<p>Hello World!")

By default, the document will be an xml.etree element instance. Whenever possible, html5lib chooses the accelerated ElementTree implementation (i.e. xml.etree.cElementTree on Python 2.x).

Two other tree types are supported: xml.dom.minidom and lxml.etree. To use an alternative format, specify the name of a treebuilder:

import html5lib
with open("mydocument.html", "rb") as f:
    lxml_etree_document = html5lib.parse(f, treebuilder="lxml")

When using with urllib2 (Python 2), the charset from HTTP should be pass into html5lib as follows:

from contextlib import closing
from urllib2 import urlopen
import html5lib

with closing(urlopen("")) as f:
    document = html5lib.parse(f,"charset"))

When using with urllib.request (Python 3), the charset from HTTP should be pass into html5lib as follows:

from urllib.request import urlopen
import html5lib

with urlopen("") as f:
    document = html5lib.parse(f,

To have more control over the parser, create a parser object explicitly. For instance, to make the parser raise exceptions on parse errors, use:

import html5lib
with open("mydocument.html", "rb") as f:
    parser = html5lib.HTMLParser(strict=True)
    document = parser.parse(f)

When you're instantiating parser objects explicitly, pass a treebuilder class as the tree keyword argument to use an alternative document format:

import html5lib
parser = html5lib.HTMLParser(tree=html5lib.getTreeBuilder("dom"))
minidom_document = parser.parse("<p>Hello World!")

More documentation is available at


html5lib works on CPython 2.7+, CPython 3.4+ and PyPy. To install it, use:

$ pip install html5lib

Optional Dependencies

The following third-party libraries may be used for additional functionality:

  • datrie can be used under CPython to improve parsing performance (though in almost all cases the improvement is marginal);
  • lxml is supported as a tree format (for both building and walking) under CPython (but not PyPy where it is known to cause segfaults);
  • genshi has a treewalker (but not builder); and
  • chardet can be used as a fallback when character encoding cannot be determined.


Please report any bugs on the issue tracker.


Unit tests require the pytest and mock libraries and can be run using the py.test command in the root directory.

Test data are contained in a separate html5lib-tests repository and included as a submodule, thus for git checkouts they must be initialized:

$ git submodule init
$ git submodule update

If you have all compatible Python implementations available on your system, you can run tests on all of them using the tox utility, which can be found on PyPI.


There's a mailing list available for support on Google Groups, html5lib-discuss, though you may get a quicker response asking on IRC in #whatwg on

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