lxml is generally distributed through PyPI.
Most Linux platforms come with some version of lxml readily packaged, usually named python-lxml for the Python 2.x version and python3-lxml for Python 3.x. If you can use that version, the quickest way to install lxml is to use the system package manager, e.g. apt-get on Debian/Ubuntu:
sudo apt-get install python3-lxml
For MacOS-X, a macport of lxml is available. Try something like
sudo port install py27-lxml
To install a newer version or to install lxml on other systems, see below.
You need Python 2.6 or later.
Unless you are using a static binary distribution (e.g. from a Windows binary installer), lxml requires libxml2 and libxslt to be installed, in particular:
Newer versions generally contain fewer bugs and are therefore recommended. XML Schema support is also still worked on in libxml2, so newer versions will give you better compliance with the W3C spec.
To install the required development packages of these dependencies on Linux systems, use your distribution specific installation tool, e.g. apt-get on Debian/Ubuntu:
sudo apt-get install libxml2-dev libxslt-dev python-dev
For Debian based systems, it should be enough to install the known build dependencies of the provided lxml package, e.g.
sudo apt-get build-dep python3-lxml
pip install lxml
If you are not using pip in a virtualenv and want to install lxml globally instead, you have to run the above command as admin, e.g. on Linux:
sudo pip install lxml
To install a specific version, either download the distribution manually and let pip install that, or pass the desired version to pip:
pip install lxml==3.4.2
To speed up the build in test environments, e.g. on a continuous integration server, disable the C compiler optimisations by setting the CFLAGS environment variable:
CFLAGS="-O0" pip install lxml
(The option reads "minus Oh Zero", i.e. zero optimisations.)
For MS Windows, recent lxml releases feature community donated binary distributions, although you might still want to take a look at the related FAQ entry. If you fail to build lxml on your MS Windows system from the signed and tested sources that we release, consider using the binary builds from PyPI or the unofficial Windows binaries that Christoph Gohlke generously provides.
On Linux (and most other well-behaved operating systems), pip will manage to build the source distribution as long as libxml2 and libxslt are properly installed, including development packages, i.e. header files, etc. See the requirements section above and use your system package management tool to look for packages like libxml2-dev or libxslt-devel. If the build fails, make sure they are installed.
Alternatively, setting STATIC_DEPS=true will download and build both libraries automatically in their latest version, e.g. STATIC_DEPS=true pip install lxml.
On MacOS-X, use the following to build the source distribution, and make sure you have a working Internet connection, as this will download libxml2 and libxslt in order to build them:
STATIC_DEPS=true sudo pip install lxml
If you want to build lxml from the GitHub repository, you should read how to build lxml from source (or the file doc/build.txt in the source tree). Building from developer sources or from modified distribution sources requires Cython to translate the lxml sources into C code. The source distribution ships with pre-generated C source files, so you do not need Cython installed to build from release sources.
If you have read these instructions and still cannot manage to install lxml, you can check the archives of the mailing list to see if your problem is known or otherwise send a mail to the list.
If you want to use lxml together with the official libxml2 Python bindings (maybe because one of your dependencies uses it), you must build lxml statically. Otherwise, the two packages will interfere in places where the libxml2 library requires global configuration, which can have any kind of effect from disappearing functionality to crashes in either of the two.
To get a static build, either pass the --static-deps option to the setup.py script, or run pip with the STATIC_DEPS or STATICBUILD environment variable set to true, i.e.
STATIC_DEPS=true pip install lxml
The STATICBUILD environment variable is handled equivalently to the STATIC_DEPS variable, but is used by some other extension packages, too.
Most MS Windows systems lack the necessarily tools to build software, starting with a C compiler already. Microsoft leaves it to users to install and configure them, which is usually not trivial and means that distributors cannot rely on these dependencies being available on a given system. In a way, you get what you've paid for and make others pay for it.
Due to the additional lack of package management of this platform, it is best to link the library dependencies statically if you decide to build from sources, rather than using a binary installer. For that, lxml can use the binary distribution of libxml2 and libxslt, which it downloads automatically during the static build. It needs both libxml2 and libxslt, as well as iconv and zlib, which are available from the same download site. Further build instructions are in the source build documentation.
If you are not using macports or want to use a more recent lxml release, you have to build it yourself. While the pre-installed system libraries of libxml2 and libxslt are less outdated in recent MacOS-X versions than they used to be, so lxml should work them them out of the box, it is still recommended to use a static build with the most recent library versions.
Luckily, lxml's setup.py script has built-in support for building and integrating these libraries statically during the build. Please read the MacOS-X build instructions.