Qt for Python Getting Started#

Important

This page is focused on building Qt for Python from source. If you just want to install PySide6, you need to run: pip install pyside6.

For more details, refer to our Quick Start guide. Additionally, you can check the FAQ related to the project.

General Requirements#

The following prerequisites must be installed before you build Qt for Python. On Linux you might get them with your operating system package manager, on macOS you might get them with brew, and on Windows you can download the installer from each website.

Guides per platform#

You can refer to the following pages for platform specific instructions:

Windows

macOS

Linux

Important

Qt for Python does not yet support WebAssembly and the mobile operating systems (Android or iOS).

Most Linux-based embedded OS provide PySide with their official package manager (for example, Raspbian and ArchlinuxARM).

A normal building command will look like this:

python setup.py install --qtpaths=/path/to/qtpaths \
                        --ignore-git \
                        --debug \
                        --build-tests \
                        --parallel=8 \
                        --verbose-build \
                        --module-subset=Core,Gui,Widgets

Which will build and install the project with debug symbols, including the tests, using ninja (instead of make), and considering only the module subset of QtCore, QtGui, and QtWidgets <PySide6.QtWidgets.

Other important options to consider are:
  • --cmake, to specify the path to the cmake binary,

  • --reuse-build, to rebuild only the modified files,

  • --openssl=/path/to/openssl/bin, to use a different path for OpenSSL,

  • --standalone, to copy over the Qt libraries into the final package to make it work on other machines,

  • --build-docs, to enable the documentation build.

  • --doc-build-online, to build documentation using the online template (by default it uses the offline)

Testing the installation#

Once the installation finishes, you will be able to execute any of our examples:

python examples/widgets/widgets/tetrix.py

Running Tests#

Using the --build-tests option will enable us to run all the auto tests inside the project:

python testrunner.py test > testlog.txt

Note

On Windows, don’t forget to have qtpaths in your path (set PATH=E:\Path\to\Qt\6.0.0\msvc2019_64\bin;%PATH%)

You can also run a specific test (for example qpainter_test) by running:

ctest -R qpainter_test --verbose

Cross Compilation#

Starting from 6.3, it is possible to cross-compile Shiboken (module), and PySide. This functionality is still in Technical Preview, which means it could change in the future releases.

Important

The only supported configuration is using a host Linux machine to cross-compile to a Linux target platform.

Cross compiling software is a valid use case that many projects rely on, however, it is a complicated process that might fail due to many reasons.

Before starting with the process, it is important to understand the details of the build system, and the goal of cross compilation.

In the build process, a Host is the computer you are currently using to compile, and a Target is your embedded device that you are compiling for.

Qt for Python is being built using setuptools, and relies on a setup.py file that is called recursively to build Shiboken (module), Shiboken (generator), and PySide. As the generator is creating the wrappers for the bindings, it’s not cross compiled for the target. Only the Shiboken (module) and PySide are cross compiled.

The building process requires a Qt installation, and a Python interpreter on both the host, and the target. The used Qt versions on both platforms should have the same minor version. That is, Qt 6.3 (host) cannot be used with a Qt 6.2 (target), or the other way around.

Note

It is recommended to use the same version of Qt on both host and target to avoid possible unconventional errors.

Prerequisites#

First and foremost, you need to have access to the target device because you need to copy several system files (sysroot). We recommend a Linux OS that has the latest Qt versions, like Manjaro ARM or Archlinux ARM.

  • (target) Install Qt 6.3+ on the system using the package manager.

  • (host) Install Qt 6.3+ on the system using the package manager or Qt Installer.

  • (target, host) Install the library and development packages that provide C++ headers, linkers, libraries, and compilers.

  • (target, host) Install Python interpreter v3.7 or later

  • (target, host) Install CMake 3.17+

After installing these prerequisites, copy the target sysroot to your host computer. This process is tricky, because copying system files from another computer might cause problems with the symbolic links. Here you have two options to achieve that.

Option A: Copying the files#

Create a directory to copy the sysroot of your target device, for example rpi-sysroot, and perform the copy on your host computer:

rsync -vR --progress -rl --delete-after --safe-links \
    USERNAME@TARGET_IP:/{lib,usr,opt/vc/lib} rpi-sysroot/

Ensure to replace USERNAME and TARGET_IP with your system appropriate values.

Option B: Packaging the file system#

Create a package for your sysroot in your target:

tar cfJ ~/sysroot.tar.xz /lib /usr /opt/vc/lib

Copy the package from the target to your host:

rsync -vR --progress USERNAME@TARGET_IP:sysroot.tar.xz .

Once you have the tar file, unpack it inside a rpi-sysroot directory.

Setting up the toolchain#

To perform the cross compilation, you need a special set of compilers, libraries, and headers, which runs on the host architecture, but generates (binaries/executables) for a target architecture. For example, from x86_64 to aarch64.

It is recommended to use the official 10.2 ARM Developer cross compilers, which you can find on their official website. For this tutorial, we choose aarch64 target architecture and we will assume that you downloaded the gcc-arm-10.2-2020.11-x86_64-aarch64-none-linux-gnu.tar.xz file, and unpacked it.

With those compilers, now you need a CMake toolchain file. This is a configuration file to set the compilers and sysroot information, together with extra options like compilation flags, and other details. You can use the following file as an example, but keep in mind they might vary:

# toolchain-aarch64.cmake
cmake_minimum_required(VERSION 3.18)
include_guard(GLOBAL)

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR aarch64)

set(TARGET_SYSROOT /path/to/your/target/sysroot)
set(CROSS_COMPILER /path/to/your/crosscompiling/compilers/)

set(CMAKE_SYSROOT ${TARGET_SYSROOT})

set(ENV{PKG_CONFIG_PATH} "")
set(ENV{PKG_CONFIG_LIBDIR} ${CMAKE_SYSROOT}/usr/lib/pkgconfig:${CMAKE_SYSROOT}/usr/share/pkgconfig)
set(ENV{PKG_CONFIG_SYSROOT_DIR} ${CMAKE_SYSROOT})

set(CMAKE_C_COMPILER ${CROSS_COMPILER}/aarch64-none-linux-gnu-gcc)
set(CMAKE_CXX_COMPILER ${CROSS_COMPILER}/aarch64-none-linux-gnu-g++)

set(QT_COMPILER_FLAGS "-march=armv8-a")
set(QT_COMPILER_FLAGS_RELEASE "-O2 -pipe")
set(QT_LINKER_FLAGS "-Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed")

set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

include(CMakeInitializeConfigs)

function(cmake_initialize_per_config_variable _PREFIX _DOCSTRING)
  if (_PREFIX MATCHES "CMAKE_(C|CXX|ASM)_FLAGS")
    set(CMAKE_${CMAKE_MATCH_1}_FLAGS_INIT "${QT_COMPILER_FLAGS}")

    foreach (config DEBUG RELEASE MINSIZEREL RELWITHDEBINFO)
      if (DEFINED QT_COMPILER_FLAGS_${config})
        set(CMAKE_${CMAKE_MATCH_1}_FLAGS_${config}_INIT "${QT_COMPILER_FLAGS_${config}}")
      endif()
    endforeach()
  endif()

  if (_PREFIX MATCHES "CMAKE_(SHARED|MODULE|EXE)_LINKER_FLAGS")
    foreach (config SHARED MODULE EXE)
      set(CMAKE_${config}_LINKER_FLAGS_INIT "${QT_LINKER_FLAGS}")
    endforeach()
  endif()

  _cmake_initialize_per_config_variable(${ARGV})
endfunction()

You need to adjust the paths in these two lines:

set(TARGET_SYSROOT /path/to/your/target/sysroot)
set(CROSS_COMPILER /path/to/your/crosscompiling/compilers/)

and replace them with the sysroot directory (the one we called rpi-sysroot), and the compilers (the gcc-arm-10.2-2020.11-x86_64-aarch64-none-linux-gnu/bin directory).

Cross compiling PySide#

After you have installed the prerequisites and copied the necessary files, you should have the following:

  • The compilers to cross compile (gcc-argm-10.2-...),

  • The target sysroot (rpi-sysroot),

  • The toolchain cmake file (toolchain-aarch64.cmake),

  • The pyside-setup repository,

An example of the setup.py invocation might look like the following:

python setup.py bdist_wheel \
    --parallel=8 --ignore-git --reuse-build --standalone --limited-api=yes \
    --cmake-toolchain-file=/opt/toolchain-aarch64.cmake \
    --qt-host-path=/opt/Qt/6.3.0/gcc_64 \
    --plat-name=linux_aarch64 \

Depending on the target platform, you could use linux_armv7, linux_aarch64, etc.

If the process succeeds, you will find the target wheels in your dist/ directory, for example:

PySide6-6.3.0-6.3.0-cp36-abi3-manylinux2014_aarch64.whl
shiboken6-6.3.0-6.3.0-cp36-abi3-manylinux2014_aarch64.whl

Troubleshooting#

  • If the auto-detection mechanism fails to find the Python or Qt installations you have in your target device, you can use two additional options:

    --python-target-path=...
    

    and:

    --qt-target-path=...
    
  • In case the automatic build of the host Shiboken (generator) fails, you can specify the custom path using:

    --shiboken-host-path=...
    

Building the documentation#

Starting from 6.3, the documentation is not being built by default. When using the second option described in this section, make sure to use the --build-docs option.

Starting from 5.15, there are two options to build the documentation:

1. Building rst-only documentation (no API)#

The process of parsing Qt headers to generate the PySide API documentation can take several minutes, this means that modifying a specific section of the rst files we currently have, might become a hard task.

For this, you can install sphinx on a virtual environment, and execute the following command:

python setup.py build_rst_docs

which will generate a html/ directory with the following structure:

html
└── pyside6
    ├── index.html
    ├── ...
    └── shiboken6
        ├── index.html
        └── ...

so you can open the main page html/pyside6/index.html on your browser to check the generated files.

This is useful when updating the general sections of the documentation, adding tutorials, modifying the build instructions, and more.

2. Building the documentation (rst + API)#

The documentation is being generated using qdoc to get the API information, and also sphinx for the local Python related notes.

The system required libxml2 and libxslt, also on the Python environment, sphinx and graphviz need to be installed before running the installation process:

pip install graphviz sphinx sphinx_tabs

After installing graphviz, the dot command needs to be in PATH, otherwise, the process will fail. Installing graphviz system-wide is also an option.

Since the process relies on a Qt installation, you need to specify where the qtbase directory is located:

export QT_SRC_DIR=/path/to/qtbase

Once the common setup.py build process finishes (remember to use --build-docs to enable the documentation build), you can go to the generated *_build/*_release/pyside6 directory, and run:

ninja apidoc

Note

The apidoc make target builds offline documentation in QCH (Qt Creator Help) format by default. You can switch to building for the online use with the --doc-build-online configure option.

The target executes several steps:

  1. The qdoc tool is run over the Qt source code to produce documentation in WebXML format.

  2. shiboken6 is run to extract the functions for which bindings exist from WebXML and convert it into RST.

  3. sphinx is run to produce the documentation in HTML format.

Re-running the command will not execute step 1 unless the file qdoc_output/webxml/qtcore-index.webxml is removed from the build tree. Similarly, step 2 will not be executed unless the file rst/PySide6/QtCore/index.rst is removed.

Finally, you will get a html directory containing all the generated documentation. The offline help files, PySide.qch and Shiboken.qch, can be moved to any directory of your choice. You can find Shiboken.qch in the build directory, *_build\*_release\shiboken6\doc\html.

If you want to temporarily change a .rst file to examine the impact on formatting, you can re-run sphinx in the doc directory:

sphinx-build rst html

Viewing offline documentation#

The offline documentation (QCH) can be viewed using the Qt Creator IDE or Qt Assistant, which is a standalone application for viewing QCH files.

To view the QCH using Qt Creator, following the instructions outlined in Using Qt Creator Help Mode. If you chose to use Qt Assistant instead, use the following command to register the QCH file before launching Qt Assistant:

assistant -register PySide.qch

Note

Qt Assistant renders the QCH content using the QTextBrowser backend, which supports a subset of the CSS styles, However, Qt Creator offers an alternative litehtml-based backend, which offers better browsing experience. At the moment, this is not the default backend, so you have to select the litehtml backend explicitly under the General tab in Qt Creator >> Tools >> Options >> Help.

Using the internal tools#

A set of tools can be found under the tools/ directory inside the pyside-setup repository.

  • checklibs.py: Script to analyze dynamic library dependencies of Mach-O binaries. To use this utility, just run:

    python checklibs.py /path/to/some.app/Contents/MacOS/Some
    

    This script was fetched from this repository.

  • create_changelog.py: Script used to create the CHANGELOG that you can find in the dist/ directory. Usage:

    python create_changelog.py -r 6.0.1 -v v6.0.0..6.0 -t bug-fix
    
  • debug_windows.py: This script can be used to find out why PySide modules fail to load with various DLL errors like Missing DLL or Missing symbol in DLL.

    You can think of it as a Windows version of ldd / LD_DEBUG.

    Underneath, it uses the cdb.exe command line debugger and the gflags.exe tool, which are installed with the latest Windows Kit.

    The aim is to help developers debug issues that they may encounter using the PySide imports on Windows. The user should then provide the generated log file.

    Incidentally it can also be used for any Windows executables, not just Python. To use it just run:

    python debug_windows.py
    
  • missing_bindings.py: This script is used to compare the state of PySide and PyQt regarding available modules and classses. This content is displayed in our wiki page, and can be used as follows:

    python missing_bindings.py --qt-version 6.0.1 -w all
    

Note

The script relies on BeautifulSoup to parse the content and generate a list of the missing bindings.