[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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