How to install PySide2 in a Python3 virtual environment on Raspberry Pi3 - virtualenv

Question

I am having a hard time installing PySide2 in a Python3 virtual enviroment on a Raspberry Pi3. I use Python-3.5.3 and the updated version of pip.
(cv3) pi#raspberrypi:~ $ which cmake
/usr/bin/cmake
(cv3) pi#raspberrypi:~ $ which qmake
/usr/bin/qmake
(cv3) pi#raspberrypi:~ $ which python
/home/pi/.virtualenvs/cv3/bin/python
(cv3) pi#raspberrypi:~ $ python --version
Python 3.5.3
(cv3) pi#raspberrypi:~ $ pip --version
pip 19.0.1 from /home/pi/.virtualenvs/cv3/lib/python3.5/site-packages/pip (python 3.5)
(cv3) pi#raspberrypi:~ $ pip3 --version
pip 19.0.1 from /home/pi/.virtualenvs/cv3/lib/python3.5/site-packages/pip (python 3.5)
First I tried to install with pip install PySide2 but I got the error
(cv3) pi#raspberrypi:~ $ pip install PySide2
Looking in indexes: https://pypi.org/simple, https://www.piwheels.org/simple
Collecting PySide2
Could not find a version that satisfies the requirement PySide2 (from versions: )
No matching distribution found for PySide2
Following the instructions found at https://wiki.qt.io/Qt_for_Python/GettingStarted on how to install via the official release wheels of Qt for Python also gives an error.
(cv3) pi#raspberrypi:~ $ pip install --index-url=https://download.qt.io/official_releases/QtForPython/ pyside2 --trusted-host download.qt.io
Looking in indexes: https://download.qt.io/official_releases/QtForPython/, https://www.piwheels.org/simple
Collecting pyside2
Could not find a version that satisfies the requirement pyside2 (from versions: )
No matching distribution found for pyside2
Then I followed the instructions on the official package site https://pypi.org/project/PySide2/. I installed the dependencies, including libclang and build from source as suggested without any errors.
git clone https://code.qt.io/pyside/pyside-setup
cd pyside-setup
git branch --track 5.12 origin/5.12
git checkout 5.12
python setup.py install --qmake=</usr/bin/qmake/> --parallel=8 --build-tests
Yet after all this work, there are no signs of the module PySide2
(cv3) pi#raspberrypi:~/pyside-setup $ python
Python 3.5.3 (default, Sep 27 2018, 17:25:39)
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import PySide2
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named 'PySide2'
>>>
Next thing I followed the instructions found on https://wiki.qt.io/Qt_for_Python/GettingStarted/X11. I clone the official repository, checked the versions are fine and then build using the qmake path /opt/Qt5.12/bin/qmake:
(cv3) pi#raspberrypi:~/pyside-setup $ python setup.py build --qmake=/opt/Qt5.12/bin/qmake --parallel=4 --build-tests --ignore-git
and the build gave two errors:
CMake Error at CMakeLists.txt:95 (message):
Unable to detect CLANG location by checking LLVM_INSTALL_DIR, CLANG_INSTALL_DIR or running llvm-config.
-- Configuring incomplete, errors occurred!
See also "/home/pi/pyside-setup/cv33_build/py3.5-qt5.12.0-32bit-release/shiboken2/CMakeFiles/CMakeOutput.log".
error: Error configuring shiboken2
I guessed perhaps updating CLANG and CMAKE will make a change. So I did the update to the latest version and the process went well without errors. Then I
While building PySide2 the process exits at 47% with the following error:
[ 47%] Linking CXX executable shiboken2
/home/pi/libclang/lib/libclang.so: file not recognized: File format not recognized
collect2: error: ld returned 1 exit status
generator/CMakeFiles/shiboken2.dir/build.make:181: set di istruzioni per l'obiettivo "generator/shiboken2" non riuscito
make[2]: *** [generator/shiboken2] Errore 1
CMakeFiles/Makefile2:2877: set di istruzioni per l'obiettivo "generator/CMakeFiles/shiboken2.dir/all" non riuscito
make[1]: *** [generator/CMakeFiles/shiboken2.dir/all] Errore 2
Makefile:140: set di istruzioni per l'obiettivo "all" non riuscito
make: *** [all] Errore 2
error: Error compiling shiboken2
Traceback (most recent call last):
File "setup.py", line 296, in <module>
setup_runner.run_setup()
File "/home/pi/pyside-setup/build_scripts/setup_runner.py", line 157, in run_setup
raise RuntimeError(msg)
RuntimeError:
setup.py invocation failed with exit code: 1.
setup.py invocation was: /home/pi/.virtualenvs/cv3/bin/python setup.py build --qmake=/opt/Qt5.12/bin/qmake --parallel=4 --build-tests --ignore-git --internal-build-type=shiboken2
Where is the problem?

Answer 1

As the version of the installed CLANG was out of date, I tried with updating it first by following the instructions found on codepool.biz. No problems arised.
Then again I pointed the LLVM and CLANG libraries to the PySide2 installation path with
export CLANG_INSTALL_DIR=/usr/local/clang_7.0.
export LLVM_INSTALL_DIR=/usr/local/clang_7.0.0
The build process successfully passed the 47% percent treeshold and finished bulding shiboken2 but got stuck at the PySide2 step at 2%. The error:
[ 2%] Built target pyside2
Makefile:140: set di istruzioni per l'obiettivo "all" non riuscito
make: *** [all] Errore 2
error: Error compiling pyside2
Traceback (most recent call last):
File "setup.py", line 296, in <module>
setup_runner.run_setup()
File "/home/pi/pyside-setup/build_scripts/setup_runner.py", line 157, in run_setup
raise RuntimeError(msg)
RuntimeError:
setup.py invocation failed with exit code: 1.
setup.py invocation was: /home/pi/.virtualenvs/cv3/bin/python setup.py build --qmake=/opt/Qt5.12/bin/qmake --parallel=4 --build-tests --ignore-git --internal-build-type=pyside2
What is going on?