Matplotlib QT backend imports not working on MacOS

[ChrFr]

What is the bug or the crash?

The imports from the matplotlib QT backend are not working on MacOS (e.g. FigureCanvasQTAgg_ or NavigationToolbar2QT from matplotlib.backends.backend_qt5agg ). I use those classes in a plugin to draw diagrams on a canvas.
The imports work fine in the Windows versions though.

There seems to be a library missing in the recent MacOS versions (?)

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg
Traceback (most recent call last):
  File "/Applications/QGIS-LTR.app/Contents/MacOS/../Resources/python/code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
  File "/Applications/QGIS-LTR.app/Contents/MacOS/../Resources/python/qgis/utils.py", line 793, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "/Applications/QGIS-LTR.app/Contents/MacOS/lib/python3.8/site-packages/matplotlib-3.3.0-py3.8-macosx-10.13.0-x86_64.egg/matplotlib/backends/backend_qt5agg.py", line 10, in <module>
    from .backend_agg import FigureCanvasAgg
  File "/Applications/QGIS-LTR.app/Contents/MacOS/../Resources/python/qgis/utils.py", line 793, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "/Applications/QGIS-LTR.app/Contents/MacOS/lib/python3.8/site-packages/matplotlib-3.3.0-py3.8-macosx-10.13.0-x86_64.egg/matplotlib/backends/backend_agg.py", line 35, in <module>
    from PIL import Image
  File "/Applications/QGIS-LTR.app/Contents/MacOS/../Resources/python/qgis/utils.py", line 793, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "/Applications/QGIS-LTR.app/Contents/MacOS/lib/python3.8/site-packages/Pillow-7.2.0-py3.8-macosx-10.13.0-x86_64.egg/PIL/Image.py", line 94, in <module>
    from . import _imaging as core
  File "/Applications/QGIS-LTR.app/Contents/MacOS/../Resources/python/qgis/utils.py", line 793, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
ImportError: dlopen(/Applications/QGIS-LTR.app/Contents/MacOS/lib/python3.8/site-packages/Pillow-7.2.0-py3.8-macosx-10.13.0-x86_64.egg/PIL/_imaging.cpython-38-darwin.so, 2): Library not loaded: /opt/X11/lib/libxcb.1.dylib
  Referenced from: /Applications/QGIS-LTR.app/Contents/MacOS/lib/python3.8/site-packages/Pillow-7.2.0-py3.8-macosx-10.13.0-x86_64.egg/PIL/_imaging.cpython-38-darwin.so
  Reason: image not found

Steps to reproduce the issue

1. Python console in QGIS (MacOS)
2. type: from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg

Versions

QGIS-Version	3.16.11-Hannover	QGIS-Codeversion	26cc1c7
Kompiliert gegen Qt	5.14.2	Laufendes Qt	5.14.2
Kompiliert mit GDAL/OGR	3.2.1	Läuft mit GDAL/OGR	3.2.1
Kompiliert mit GEOS	3.9.1-CAPI-1.14.2	Läuft mit GEOS	3.9.1-CAPI-1.14.2
Kompiliert mit SQLite	3.31.1	Läuft mit SQLite	3.31.1
PostgreSQL-Client-Version	12.3	SpatiaLite-Version	4.3.0a
QWT-Version	6.1.4	QScintilla2-Version	2.11.4
Kompiliert mit PROJ	6.3.2	Läuft mit PROJ	Rel. 6.3.2, May 1st, 2020
BS-Version	macOS 10.15
Aktive Python-Erweiterungen	QuickOSM; quick_map_services; nominatim; mmqgis; processing; db_manager; MetaSearch

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response

[PeterPetrik]

Hi @ChrFr thank you for your bug-report. Could you please download nightly build https://qgis.org/downloads/macos/nightly/qgis_nightly_master_20211004_123226.dmg and let me know if the issue still persists?

also could you please run command in terminal and submit me here the output?

otool -L /Applications/QGIS-LTR.app/Contents/MacOS/lib/python3.8/site-packages/Pillow-7.2.0-py3.8-macosx-10.13.0-x86_64.egg/PIL/_imaging.cpython-38-darwin.so

[ChrFr]

Hi @PeterPetrik,

thank you for the fast response! The imports work with the linked nightly build 👍.

the output of the otool command:

/Applications/QGIS-LTR.app/Contents/MacOS/lib/python3.8/site-packages/Pillow-7.2.0-py3.8-macosx-10.13.0-x86_64.egg/PIL/_imaging.cpython-38-darwin.so:
@rpath/libjpeg.9.dylib (compatibility version 14.0.0, current version 14.0.0)
@rpath/libopenjp2.7.dylib (compatibility version 7.0.0, current version 2.3.1)
@rpath/libz.1.dylib (compatibility version 1.0.0, current version 1.2.11)
@rpath/libtiff.5.dylib (compatibility version 11.0.0, current version 11.0.0)
/opt/X11/lib/libxcb.1.dylib (compatibility version 3.0.0, current version 3.0.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1292.60.1)

thanks

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