[QGIS-Developer] Building QGIS with QT6 on Ubuntu: Python error at start

Richard Duivenvoorde rdmailings at duif.net
Wed Jul 23 00:11:47 PDT 2025


Mmm, yes I should have sent this one too:

sudo apt-get install python3 git bison ninja-build build-essential ca-certificates ccache cmake cmake-curses-gui dh-python doxygen expect flex flip gdal-bin grass-dev libexiv2-dev libexpat1-dev libfcgi-dev libgdal-dev libgeos-dev libgsl-dev libpq-dev libproj-dev libzip-dev libprotobuf-dev libspatialindex-dev libdraco-dev python3-dev python3-pyqt6.sip libxkbcommon-dev protobuf-compiler sip-tools spawn-fcgi xauth xfonts-100dpi xfonts-75dpi xfonts-base xfonts-scalable xvfb python3-pyqtbuild    libqca-qt6-dev qtkeychain-qt6-dev libqscintilla2-qt6-dev qt6-serialport-dev qt6-svg-dev qt6-positioning-dev libqt6core5compat6 qt6-5compat-dev python3-pyqt6 python3-pyqt6.qsci pyqt6-dev-tools python3-pyqt6.qtmultimedia qml6-module-qtmultimedia qt6-multimedia-dev qt6-tools-dev pyqt6-dev pyqt6.qsci-dev python3-pyqt6.qtpositioning python3-pyqt6.qtserialport python3-pyqt6.qtsvg

As you can see I install the multimedia stuff already, so that is probably the reason it 'just worked'(TM) with me :-)

Glad this is fixed!

Regards,
Richard Duivenvoorde

On 22-07-2025 09:00, Alessandro Pasotti wrote:
> Thank you Richard,
> 
> your workflow is almost exactly the same I am doing.
> 
> With the help of Nyall I have been able to track down the issue to a missing packagepython3-pyqt6.qtmultimedia.
> 
> The debugging process involved removing all the imports from
> 
> https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui.sip.in <https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui.sip.in>
> 
> and find the broken piece, to my surprise, removing the lines highlighted here
> https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui.sip.in#L16C1-L20C22 <https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui.sip.in#L16C1-L20C22>
> 
> eventually led to a readable error message (QtMultimedia could not be imported) instead of the corrupted one.
> 
> Why the error message gets corrupted after qsci is imported (or after
> https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui_auto.sip <https://github.com/qgis/QGIS/blob/master/python/PyQt6/gui/gui_auto.sip> is imports, I don't know which one is responsible of the issue) still remains a mystery to me.
> 
> Thank you all for the help!
> 
> 
> 
> On Mon, Jul 21, 2025 at 8:23 PM Richard Duivenvoorde <rdmailings at duif.net <mailto:rdmailings at duif.net>> wrote:
> 
>     I'm on Trixie (next stable in a couple of weeks), and only build QWT myself from source:
> 
>        # https://qwt.sourceforge.io/qwtinstall.html <https://qwt.sourceforge.io/qwtinstall.html>
>        # download the tar.bz2 from https://sourceforge.net/projects/qwt/files/qwt/6.3.0/ <https://sourceforge.net/projects/qwt/files/qwt/6.3.0/>
>        # unpack and go into ~/git/qwt-6.3.0 dir
>        # error: qmake: could not find a Qt installation of ''  -> https://askubuntu.com/questions/1460242/ubuntu-22-04-with-qt6-qmake-could-not-find-a-qt-installation-of <https://askubuntu.com/questions/1460242/ubuntu-22-04-with-qt6-qmake-could-not-find-a-qt-installation-of>?
>        qtchooser -install qt6 $(which qmake6)
>        export QT_SELECT=qt6
>        # create Makefile
>        /usr/bin/qmake qwt.pro <http://qwt.pro>
>        # compile
>        make
>        # install (in /usr/local/qwt-6.3.0 )
>        sudo make install
> 
>     Then, leaving out a lot of stuff...:
> 
>     mkdir buildqt6;cd buildqt6;ccmake -GNinja -DBUILD_TESTING=FALSE -DENABLE_TESTS=OFF -DWITH_SERVER=FALSE -DWITH_3D=FALSE -DCMAKE_INSTALL_PREFIX=/home/richard/bin/qgis_/qt6/debug -DWITH_QWTPOLAR=OFF -DCMAKE_BUILD_TYPE=Debug -DWITH_GRASS=FALSE -DBUILD_WITH_QT6=TRUE -DWITH_OAUTH2_PLUGIN=FALSE -DWITH_WITH_SERVER_PLUGINS=OFF -DWITH_STAGED_PLUGINS=OFF -DWITH_PDAL=OFF -DWITH_QTWEBKIT=OFF -DQWT_INCLUDE_DIR=/usr/local/qwt-6.3.0/include  -DQWT_LIBRARY=/usr/local/qwt-6.3.0/lib/libqwt.so  ..
> 
>     in the same git repo as my qt5 build, QGIS works.
> 
>     I'm on python 3.13.5 here
> 
>     Not sure if this helps...
> 
>     Richard
> 
> 
> 
> 
>     On 21-07-2025 17:52, Alessandro Pasotti via QGIS-Developer wrote:
>      >
>      > Thanks, I'm using Python 3.13 (that comes with that Ubuntu version).
>      >
>      > Now I'm trying with vcpkg ...
>      >
>      >
>      > On Mon, Jul 21, 2025 at 5:35 PM pathmapper <pathmapper at posteo.de <mailto:pathmapper at posteo.de> <mailto:pathmapper at posteo.de <mailto:pathmapper at posteo.de>>> wrote:
>      >
>      >     Hi,
>      >
>      >     I don't know what's wrong, but when I had similar problems, switching to
>      >     Python 3.12 solved them for me.
>      >
>      >     Cheers,
>      >     Björn
>      >
>      >     On 21.07.2025 16:58, Alessandro Pasotti via QGIS-Developer wrote:
>      >      > Hi,
>      >      >
>      >      > I am trying to build QGIS with QT6 on Ubuntu (tried 24.10 and 25.04),
>      >      > it builds without errors but when I run it, the following error
>      >      > appears:
>      >      >
>      >      > Couldn't load PyQGIS.
>      >      > Python support will be disabled.
>      >      >
>      >      > Traceback (most recent call last):
>      >      >   File "", line 1, in
>      >      >   File
>      >      > "/home/ale/dev/QGIS/build/Desktop_QT6-Debug/output/python/qgis/gui/__init__.py",
>      >      > line 25, in
>      >      >     from qgis._gui import *
>      >      > RuntimeError: qgis._gui cannot import type '���A� ' from
>      >      > PyQt6.QtCore
>      >      >
>      >      > Python version:
>      >      > 3.13.3 (main, Jun 16 2025, 18:15:32) [GCC 14.2.0]
>      >      >
>      >      > QGIS version:
>      >      > 3.99.0-Master 'Master', e717e3cd2b9
>      >      >
>      >      > Python path:
>      >      > ['/home/ale/dev/QGIS/build/Desktop_QT6-Debug/output/python',
>      >      > '/home/ale/.local/share/QGIS/QGIS3/profiles/default/python',
>      >      > '/home/ale/.local/share/QGIS/QGIS3/profiles/default/python/plugins',
>      >      > '/home/ale/dev/QGIS/build/Desktop_QT6-Debug/output/python/plugins',
>      >      > '/home/ale/dev/gdal/desktop-install/local/lib/python3.13/dist-packages',
>      >      > '/home/ale/dev/gdal/autotest/pymod', '/usr/lib/python313.zip',
>      >      > '/usr/lib/python3.13', '/usr/lib/python3.13/lib-dynload',
>      >      > '/usr/local/lib/python3.13/dist-packages',
>      >      > '/usr/lib/python3/dist-packages']
>      >      >
>      >      > I checked the QGIS/build/Desktop_QT6-Debug/output/python/qgis content
>      >      > and it looks legit.
>      >      >
>      >      > PyQt6 installation also looks ok, importing core works ok, only gui
>      >      > does not work.
>      >      >
>      >      > Any idea about what's going wrong?
>      >      >
>      >      > --
>      >      >
>      >      > Alessandro Pasotti
>      >      > QCooperative: www.qcooperative.net <http://www.qcooperative.net> <http://www.qcooperative.net <http://www.qcooperative.net>> [1]
>      >      > ItOpen: www.itopen.it <http://www.itopen.it> <http://www.itopen.it <http://www.itopen.it>> [2]
>      >      >
>      >      > Links:
>      >      > ------
>      >      > [1] https://www.qcooperative.net <https://www.qcooperative.net> <https://www.qcooperative.net <https://www.qcooperative.net>>
>      >      > [2] http://www.itopen.it <http://www.itopen.it> <http://www.itopen.it <http://www.itopen.it>>
>      >      >
>      >      > _______________________________________________
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>      >
>      >
>      >
>      > --
>      > Alessandro Pasotti
>      > QCooperative: www.qcooperative.net <http://www.qcooperative.net> <https://www.qcooperative.net <https://www.qcooperative.net>>
>      > ItOpen: www.itopen.it <http://www.itopen.it> <http://www.itopen.it <http://www.itopen.it>>
>      >
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> 
> 
> -- 
> Alessandro Pasotti
> QCooperative: www.qcooperative.net <https://www.qcooperative.net>
> ItOpen: www.itopen.it <http://www.itopen.it>



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