No working GUI backend found for matplotlib

[andrersimoes]

I can't change PyPlot's backend from :tk to :qt5 after a fresh install:

bash> julia
julia> using PyCall
julia> pygui( :qt5 )

julia> pyimport( "matplotlib" )
PyObject <module 'matplotlib' from '/home/simoes/.local/lib/python3.10/site-packages/matplotlib/init.py'>

julia> pyimport( "PyQt5" )
PyObject <module 'PyQt5' from '/usr/lib64/python3.10/site-packages/PyQt5/init.py'>

julia> using PyPlot
┌ Warning: No working GUI backend found for matplotlib
└ @ PyPlot ~/.julia/packages/PyPlot/NsAWt/src/init.jl:153

My configuration:

1. OpenSuse tumbleweed.
2. pyqt 5.15.7
3. matplotlib 3.5.2

PS: PyQt5 backend works fine when directly called from python command prompt.

My installation steps are:

1. rm -rf .julia to avoid old trash;
2. open julia;
3. define ENV[ "PYTHON"] = "/usr/bin/python3.10";
4. add package PyCall;
5. add package PyPlot;
6. attempt to use as :tk success;
7. restart julia
8. include PyCall
9. change backend to :qt5
10. include PyPlot
11. backend not available.

Any suggestions ?

[stevengj]

You definitely should not do pyimport("matplotlib") before doing using PyPlot — importing matplotlib initializes it, and it won't subsequently be possible to change backends. What happens if you do just:

ENV["MPLBACKEND"]="Qt5Agg"
using PyPlot

[andrersimoes]

Hi Steve, didn't know about it. I was just trying to show you that the required packages (matplotlib and qt) are installed on my system. But even without calling pyimport, the results are the same.

If i reset julia and do ENV["MPLBACKEND"]="Qt5Agg" before using PyPlot it plots with the toolbar on the bottom (tk environment).

Do you have any other suggestion ?

[andrersimoes]

Hi Steve, i tried to:

1. force gui = :qt5 inside PyCall source code gui.jl;
2. do several prints inside find_backend.
3. print the exception from the try catch block inside find_backend.

This happens:

bash> julia
julia> using PyCall
julia> PyCall.gui
:qt5
julia> using PyPlot
find_backend 1
find_backend 2
find_backend 3 qt5agg
find_backend 5
find_backend 6
find_backend 6.1
exception UndefVarError(:gui)
find_backend 13
┌ Warning: No working GUI backend found for matplotlib
└ @ PyPlot ~/.julia/packages/PyPlot/NsAWt/src/init.jl:178

Sounds like PyPlot cannot find PyCall.gui

My init.jl goes attached as a text file so you can see where are my println's:
init.txt

PS: println from line 164 is in the wrong position (put it after gui = pygui() to avoid catch)

[andrersimoes]

Hi Steve,

I could fix the problem after doing some extra prints inside find_backend, upgrading pip and installing PySide2:

bash> python3 -m pip install --upgrade pip
... reinstallation of PyQt5
bash> pip3 install -U PySide2

The strange part was that PyQt5 was already installed at my machine.

Last exception goes attached for reference.
exception.txt

[stevengj]

That's a bit odd. PyPlot/init.jl does not even look for PySide2, so I'm confused.