[QGIS-Developer] Building QGIS with QT6 on Ubuntu: Python error at start
Werner Macho
werner.macho at gmail.com
Tue Jul 22 23:25:31 PDT 2025
Hi Alessandro!
Thanks for sharing that .. that was exactly the package missing here too,
but out of the error message I would have never imagined that there is
something missing.
Everything is working here too, maybe it is possible to get a meaningful
error message somehow when this happens?
thanks again and regards
Werner
On Tue, Jul 22, 2025 at 9:01 AM Alessandro Pasotti via QGIS-Developer <
qgis-developer at lists.osgeo.org> 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 package python3-pyqt6.qtmultimedia.
>
> The debugging process involved removing all the imports from
>
> 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
>
> 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 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>
> 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
>> # download the tar.bz2 from
>> 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
>> ?
>> qtchooser -install qt6 $(which qmake6)
>> export QT_SELECT=qt6
>> # create Makefile
>> /usr/bin/qmake 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>> 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>
>> [1]
>> > > ItOpen: www.itopen.it <http://www.itopen.it> [2]
>> > >
>> > > Links:
>> > > ------
>> > > [1] https://www.qcooperative.net <https://www.qcooperative.net>
>> > > [2] http://www.itopen.it <http://www.itopen.it>
>> > >
>> > > _______________________________________________
>> > > QGIS-Developer mailing list
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>> QGIS-Developer at lists.osgeo.org>
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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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>>
>
> --
> Alessandro Pasotti
> QCooperative: www.qcooperative.net
> ItOpen: www.itopen.it
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