Matplotlib no longer supports qt4 nor gtk backends

[oscargus]

Issue Report Checklist

• Searched the issues page for similar reports
• Read the relevant sections of the Spyder Troubleshooting Guide and followed its advice
• Reproduced the issue after updating with conda update spyder (or pip, if not using Anaconda)
• Could not reproduce inside jupyter qtconsole (if console-related)
• Tried basic troubleshooting (if a bug/error)
  • Restarted Spyder
  • Reset preferences with spyder --reset
  • Reinstalled the latest version of Anaconda
  • Tried the other applicable steps from the Troubleshooting Guide
• Completed the Problem Description, Steps to Reproduce and Version sections below

Problem Description

With version 3.5.0 the qt4 support is completely dropped in matplotlib (qt6 is supported though).

This is what happens when starting a console with qt4 set:

Output from spyder call 'show_mpl_backend_errors':

=========================================================================
NOTE: The following error appeared when setting your Matplotlib backend!!
=========================================================================

Traceback (most recent call last):
  File "/usr/lib/python3.10/site-packages/spyder_kernels/console/kernel.py", line 723, in _set_mpl_backend
    get_ipython().run_line_magic(magic, backend)
  File "/usr/lib/python3.10/site-packages/IPython/core/interactiveshell.py", line 2364, in run_line_magic
    result = fn(*args, **kwargs)
  File "/usr/lib/python3.10/site-packages/decorator.py", line 232, in fun
    return caller(func, *(extras + args), **kw)
  File "/usr/lib/python3.10/site-packages/IPython/core/magic.py", line 187, in <lambda>
    call = lambda f, *a, **k: f(*a, **k)
  File "/usr/lib/python3.10/site-packages/IPython/core/magics/pylab.py", line 99, in matplotlib
    gui, backend = self.shell.enable_matplotlib(args.gui.lower() if isinstance(args.gui, str) else args.gui)
  File "/usr/lib/python3.10/site-packages/IPython/core/interactiveshell.py", line 3546, in enable_matplotlib
    pt.activate_matplotlib(backend)
  File "/usr/lib/python3.10/site-packages/IPython/core/pylabtools.py", line 352, in activate_matplotlib
    matplotlib.rcParams['backend'] = backend
  File "/home/oscar/dev/matplotlib/lib/matplotlib/__init__.py", line 644, in __setitem__
    raise ValueError(f"Key {key}: {ve}") from None
ValueError: Key backend: 'qt4agg' is not a valid value for backend; supported values are ['GTK3Agg', 'GTK3Cairo', 'GTK4Agg', 'GTK4Cairo', 'MacOSX', 'nbAgg', 'QtAgg', 'QtCairo', 'Qt5Agg', 'Qt5Cairo', 'TkAgg', 'TkCairo', 'WebAgg', 'WX', 'WXAgg', 'WXCairo', 'agg', 'cairo', 'pdf', 'pgf', 'ps', 'svg', 'template']

Similar error message with gtk.

I may be tempted to go for a PR, but how should one deal with different versions etc? If a user has a pre 3.5.0-version it will still work, so just removing them may not be the obvious solution?

What steps reproduce the problem?

1. Open preferences
2. Change IPython/Graphics to qt4 or gtk
3. Start a new console

What is the expected output? What do you see instead?

No error messages = remove gtk and qt4 options.

Paste Traceback/Error Below (if applicable)

PASTE TRACEBACK HERE

Versions

• Spyder version: 5.2.0 None
• Python version: 3.10.1 64-bit
• Qt version: 5.15.2
• PyQt5 version: 5.15.6
• Operating System: Linux 5.12.9-arch1-1

Dependencies

# Mandatory:
atomicwrites >=1.2.0          :  1.4.0 (OK)
chardet >=2.0.0               :  4.0.0 (OK)
cloudpickle >=0.5.0           :  2.0.0 (OK)
cookiecutter >=1.6.0          :  1.7.3 (OK)
diff_match_patch >=20181111   :  20200713 (OK)
intervaltree >=3.0.2          :  3.1.0 (OK)
IPython >=7.6.0               :  7.31.0 (OK)
jedi >=0.17.2;<0.19.0         :  0.18.1 (OK)
jellyfish >=0.7               :  0.9.0 (OK)
jsonschema >=3.2.0            :  3.2.0 (OK)
keyring >=17.0.0              :  23.4.0 (OK)
nbconvert >=4.0               :  6.1.0 (OK)
numpydoc >=0.6.0              :  1.1.0 (OK)
parso >=0.7.0;<0.9.0          :  0.8.2 (OK)
pexpect >=4.4.0               :  4.8.0 (OK)
pickleshare >=0.4             :  0.7.5 (OK)
psutil >=5.3                  :  5.9.0 (OK)
pygments >=2.0                :  2.11.2 (OK)
pylint >=2.5.0                :  2.12.2 (OK)
pyls_spyder >=0.4.0           :  0.4.0 (OK)
pylsp >=1.3.1;<1.4.0          :  1.3.2 (OK)
pylsp_black >=1.0.0           :  None (OK)
qdarkstyle >=3.0.2            :  3.0.2 (OK)
qstylizer >=0.1.10            :  0.2.1 (OK)
qtawesome >=1.0.2             :  1.0.3 (OK)
qtconsole >=5.2.1;<5.3.0      :  5.2.1 (OK)
qtpy >=1.5.0                  :  1.11.2 (OK)
rtree >=0.9.7                 :  0.9.7 (OK)
setuptools >=49.6.0           :  59.1.0 (OK)
sphinx >=0.6.6                :  4.3.2 (OK)
spyder_kernels >=2.2.0;<2.3.0 :  2.2.0 (OK)
textdistance >=4.2.0          :  4.2.2 (OK)
three_merge >=0.1.1           :  0.1.1 (OK)
watchdog >=0.10.3             :  0.10.7 (OK)
xdg >=0.26                    :  0.27 (OK)
zmq >=17                      :  22.2.1 (OK)

# Optional:
cython >=0.21                 :  None (OK)
matplotlib >=2.0.0            :  3.6.0.dev1303+g8d7a2b9d2a.d20220111 (OK)
numpy >=1.7                   :  1.21.5 (OK)
pandas >=1.1.1                :  None (OK)
scipy >=0.17.0                :  1.7.3 (OK)
sympy >=0.7.3                 :  1.10.dev (OK)

[oscargus]

I have now tried to sort things out and as a consequence of not sorting it out, read up a bit. I realize that it comes down to ipython/ipykernel#775 (where @ccordoba12 has commented, so you are well aware of it).

Anyway, removing qt4 and gtk (and always enabling wx since it is not PY2 only anymore) may be an option so far. Let me know if you want a PR for that part.

[ccordoba12]

Hey @oscargus, thanks for reporting. I also noticed this problem recently and my plan is to fix it in Spyder 5.3.

Let me know if you want a PR for that part.

Thanks for the offer! But since this also requires a synced PR on spyder-kernels, I prefer to do it myself.