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What's new in lxml 2.0?
.. contents::
1 Changes in etree and objectify
1.1 Incompatible changes
1.2 Enhancements
1.3 Other changes
2 New modules
2.1 lxml.html
2.2 lxml.cssselect
2.3 lxml.doctestcompare
During the development of the lxml 1.x series, a couple of quirks were
discovered in the design that made the API less obvious and its future
extensions harder than necessary. lxml 2.0 is a soft evolution of lxml 1.x
towards a simpler, more consistent and more powerful API - with some major
extensions. Wherever possible, lxml 1.3 comes close to the semantics of lxml
2.0, so that migrating should be easier for code that currently runs with 1.3.
Changes in etree and objectify
A graduation towards a more consistent API cannot go without a certain amount
of incompatible changes. The following is a list of those differences that
applications need to take into account when migrating from lxml 1.x to lxml
Incompatible changes
* lxml 0.9 introduced a feature called `namespace implementation`_. The
global ``Namespace`` factory was added to register custom element classes
and have lxml.etree look them up automatically. However, the later
development of further class lookup mechanisms made it appear less and less
adequate to register this mapping at a global level, so lxml 1.1 first
removed the namespace based lookup from the default setup and lxml 2.0
finally removes the global namespace registry completely. As all other
lookup mechanisms, the namespace lookup is now local to a parser, including
the registry itself. Applications that use a module-level parser can easily
map its ``get_namespace()`` method to a global ``Namespace`` function to
mimic the old behaviour.
.. _`namespace implementation`: element_classes.html#implementing-namespaces
* XPath now raises exceptions specific to the part of the execution that
failed: ``XPathSyntaxError`` for parser errors and ``XPathEvalError`` for
errors that occurred during the evaluation. Note that the distinction only
works for the ``XPath()`` class. The other two evaluators only have a
single evaluation call that includes the parsing step, and will therefore
only raise an ``XPathEvalError``. Applications can catch both exceptions
through the common base class ``XPathError`` (which also exists in earlier
lxml versions).
* Network access in parsers is now disabled by default, i.e. the
``no_network`` option defaults to True. Due to a somewhat 'interesting'
implementation in libxml2, this does not affect the first document (i.e. the
URL that is parsed), but only subsequent documents, such as a DTD when
parsing with validation. This means that you will have to check the URL you
pass, instead of relying on lxml to prevent *any* access to external
resources. As this can be helpful in some use cases, lxml does not work
around it.
* The type annotations in lxml.objectify (the ``pytype`` attribute) now use
``NoneType`` for the None value as this is the correct Python type name.
Previously, lxml 1.x used a lower case ``none``.
* Another change in objectify regards the way it deals with ambiguous types.
Previously, setting a value like the string ``"3"`` through normal attribute
access would let it come back as an integer when reading the object
attribute. lxml 2.0 prevents this by always setting the ``pytype``
attribute to the type the user passed in, so ``"3"`` will come back as a
string, while the number ``3`` will come back as a number. To remove the
type annotation on serialisation, you can use the ``deannotate()`` function.
* The C-API function ``findOrBuildNodeNs()`` was replaced by the more generic
Most of the enhancements of lxml 2.0 were made under the hood. Most people
won't even notice them, but they make the maintenance of lxml easier and thus
facilitate further enhancements and an improved integration between lxml's
* lxml.objectify now has its own implementation of the `E factory`_. It uses
the built-in type lookup mechanism of lxml.objectify, thus removing the need
for an additional type registry mechanism (as previously available through
the ``typemap`` parameter).
* XML entities are supported through the ``Entity()`` factory, an Entity
element class and a parser option ``resolve_entities`` that allows to keep
entities in the element tree when set to False. Also, the parser will now
report undefined entities as errors if it needs to resolve them (which is
still the default, as in lxml 1.x).
* A major part of the XPath code was rewritten and can now benefit from a
bigger overlap with the XSLT code. The main benefits are improved thread
safety in the XPath evaluators and Python RegExp support in standard XPath.
.. _`E factory`: objectify.html#tree-generation-with-the-e-factory
New modules
The most visible changes in lxml 2.0 regard the new modules that were added.
A very useful module for doctests based on XML or HTML is
``lxml.doctestcompare``. It provides a relaxed comparison mechanism for XML
and HTML in doctests. Using it is as simple as::
>>> import lxml.usedoctest
for XML comparisons and::
>>> import lxml.html.usedoctest
for HTML comparisons.
The largest new package that was added to lxml 2.0 is `lxml.html`_. It
contains various tools and modules for HTML handling. The major features
include support for cleaning up HTML (removing unwanted content), a readable
HTML diff and various tools for working with links.
.. _`lxml.html`: lxmlhtml.html
The Cascading Stylesheet Language (CSS_) has a very short and generic path
language for pointing at elements in XML/HTML trees (`CSS selectors`_). The module
lxml.cssselect_ provides an implementation based on XPath.
.. _lxml.cssselect: cssselect.html
.. _CSS:
.. _`CSS selectors`:
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