SIP is a tool that makes it very easy to create Python bindings for C and C++ libraries. It was originally developed to create PyQt, the Python bindings for the Qt toolkit, but can be used to create bindings for any C or C++ library.

SIP comprises a code generator and a Python module. The code generator processes a set of specification files and generates C or C++ code which is then compiled to create the bindings extension module. The SIP Python module provides support functions to the automatically generated code.


The SIPBuilder and SIPPackage base classes come with the following phases:

  1. configure - configure the package

  2. build - build the package

  3. install - install the package

By default, these phases run:

$ python --bindir ... --destdir ...
$ make
$ make install

Important files

Each SIP package comes with a custom build script, written in Python. This script contains instructions to build the project.

Build system dependencies

SIPPackage requires several dependencies. Python is needed to run the build script, and to run the resulting Python libraries. Qt is needed to provide the qmake command. SIP is also needed to build the package. All of these dependencies are automatically added via the base class


depends_on('qt', type='build')

depends_on('py-sip', type='build')

Passing arguments to

Each phase comes with a <phase_args> function that can be used to pass arguments to that particular phase. For example, if you need to pass arguments to the configure phase, you can use:

def configure_args(self, spec, prefix):
    return ['--no-python-dbus']

A list of valid options can be found by running python --help.


Just because a package successfully built does not mean that it built correctly. The most reliable test of whether or not the package was correctly installed is to attempt to import all of the modules that get installed. To get a list of modules, run the following command in the site-packages directory:

$ python
>>> import setuptools
>>> setuptools.find_packages()
    'PyQt5', 'PyQt5.QtCore', 'PyQt5.QtGui', 'PyQt5.QtHelp',
    'PyQt5.QtMultimedia', 'PyQt5.QtMultimediaWidgets', 'PyQt5.QtNetwork',
    'PyQt5.QtOpenGL', 'PyQt5.QtPrintSupport', 'PyQt5.QtQml',
    'PyQt5.QtQuick', 'PyQt5.QtSvg', 'PyQt5.QtTest', 'PyQt5.QtWebChannel',
    'PyQt5.QtWebSockets', 'PyQt5.QtWidgets', 'PyQt5.QtXml',

Large, complex packages like py-pyqt5 will return a long list of packages, while other packages may return an empty list. These packages only install a single file. In Python packaging lingo, a “package” is a directory containing files like:


whereas a “module” is a single Python file.

The SIPPackage base class automatically detects these module names for you. If, for whatever reason, the module names detected are wrong, you can provide the names yourself by overriding import_modules like so:

import_modules = ['PyQt5']

These tests often catch missing dependencies and non-RPATHed libraries. Make sure not to add modules/packages containing the word “test”, as these likely won’t end up in the installation directory, or may require test dependencies like pytest to be installed.

These tests can be triggered by running spack install --test=root or by running spack test run after the installation has finished.

External documentation

For more information on the SIP build system, see: