Fix the Qt4/Qt5 port that left the app unable to start, and modernise the template

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.9", "3.11", "3.12"]
+
+    steps:
+      - uses: actions/checkout@v5
+
+      - uses: actions/setup-python@v6
+        with:
+          python-version: ${{ matrix.python-version }}
+          cache: pip
+
+      # PyQt5 wheels bundle Qt itself but still link against these system
+      # libraries, which the GitHub runner image does not ship. They are
+      # needed even for the offscreen platform plugin.
+      - name: Install Qt system libraries
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            libegl1 libgl1 libdbus-1-3 libxkbcommon-x11-0 \
+            libxcb-icccm4 libxcb-image0 libxcb-keysyms1 libxcb-randr0 \
+            libxcb-render-util0 libxcb-shape0 libxcb-xfixes0 libxcb-xinerama0
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+          pip install pytest
+
+      - name: Run tests
+        env:
+          QT_QPA_PLATFORM: offscreen
+        run: pytest
+
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - uses: actions/setup-python@v6
+        with:
+          python-version: "3.12"
+      - run: pip install ruff
+      - run: ruff check .

.gitignore

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+# Byte-compiled / optimised files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# Distribution / packaging
+build/
+dist/
+*.egg-info/
+.eggs/
+
+# Virtual environments
+.venv/
+venv/
+env/
+
+# Test / coverage artefacts
+.pytest_cache/
+.coverage
+coverage.xml
+htmlcov/
+
+# Editors and OS cruft
+.idea/
+.vscode/
+.DS_Store

CommonMPL.py

@@ -1,113 +1,83 @@
-#!/usr/bin/python
-# -*- coding: utf-8 -*-
-# Pierre Haessig — March 2014
-"""
-Qt adaptation of Gael Varoquaux's tutorial to integrate Matplotlib
-http://docs.enthought.com/traitsui/tutorials/traits_ui_scientific_app.html#extending-traitsui-adding-a-matplotlib-figure-to-our-application
-based on Qt-based code shared by Didrik Pinte, May 2012
-http://markmail.org/message/z3hnoqruk56g2bje
-adapted and tested to work with PySide from Anaconda in March 2014
-"""
+#!/usr/bin/env python3
+"""A TraitsUI editor that embeds a matplotlib figure in a Qt5 application.
 
-from pyface.qt import QtGui, QtCore
-#from traits.etsconfig.api import ETSConfig
-#ETSConfig.toolkit = 'qt4'
-#
-import matplotlib as mpl
-#mpl.rcParams['backend.qt4']='PySide'
-# We want matplotlib to use a QT backend
-mpl.use('Qt4Agg')
-from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
-from matplotlib.figure import Figure
-from matplotlib.backends.backend_qt4agg import NavigationToolbar2QT
-
-from traits.api import Any, Instance
-from traitsui.qt4.editor import Editor
-from traitsui.qt4.basic_editor_factory import BasicEditorFactory
-from traitsui.api import Handler
+Originally a Qt adaptation by Pierre Haessig (March 2014) of Gael Varoquaux's
+tutorial on integrating matplotlib with TraitsUI, based on Qt code shared by
+Didrik Pinte (May 2012):
 
+* http://docs.enthought.com/traitsui/tutorials/traits_ui_scientific_app.html
+* http://markmail.org/message/z3hnoqruk56g2bje
+* https://gist.github.com/pierre-haessig/9838326
 
+Import order matters here. ``pyface.qt`` is imported first so that it resolves
+and caches the Qt binding (PyQt5, PySide2, ...); matplotlib then reuses the
+already-imported binding instead of independently picking a different one,
+which would crash the moment the two tried to share a widget.
+"""
 
-from traits.api import *
-from traitsui.api import View,UItem, Item, Group, Heading, Label, \
-        HSplit, Handler, CheckListEditor, EnumEditor, TableEditor, FileEditor, \
-        ListEditor, Tabbed, VGroup, HGroup, RangeEditor, Spring, spring
-from traitsui.menu import NoButtons
+# isort: off
+# Order is deliberate -- see the module docstring. pyface.qt must resolve the
+# Qt binding before matplotlib looks for one. Do not let a formatter sort these.
+from pyface.qt import QtGui
 
-#from traitsui.wx.editor import Editor
-from traitsui.api import ColorTrait
+from matplotlib.backends.backend_qtagg import (
+    FigureCanvasQTAgg as FigureCanvas,
+    NavigationToolbar2QT as NavigationToolbar,
+)
 
-import numpy as np
-from matplotlib import *
-import os,sys,platform,socket,random
+# isort: on
 
-class _MPLFigureEditor(Editor):
+from traitsui.api import Handler
+from traitsui.basic_editor_factory import BasicEditorFactory
+from traitsui.qt.editor import Editor
 
-   scrollable  = True
+__all__ = ["MPLFigureEditor", "MPLInitHandler"]
 
-   def init(self, parent):
-       self.control = self._create_canvas(parent)
-       self.set_tooltip()
 
-   def update_editor(self):
-       pass
+class _MPLFigureEditor(Editor):
+    """Wraps a :class:`~matplotlib.figure.Figure` trait in a Qt canvas."""
 
-   def _create_canvas(self, parent):
-       """ Create the MPL canvas. """
-       # matplotlib commands to create a canvas
-       frame = QtGui.QWidget()
-       mpl_canvas = FigureCanvas(self.value)
-       mpl_canvas.setParent(frame)
-       mpl_toolbar = NavigationToolbar2QT(mpl_canvas,frame)
+    scrollable = True
 
-       vbox = QtGui.QVBoxLayout()
-       vbox.addWidget(mpl_canvas)
-       vbox.addWidget(mpl_toolbar)
-       frame.setLayout(vbox)
+    def init(self, parent):
+        self._canvas = None
+        self.control = self._create_canvas(parent)
+        self.set_tooltip()
 
-       return frame
+    def update_editor(self):
+        """Redraw the canvas when the underlying figure trait changes."""
+        if self._canvas is not None:
+            self._canvas.draw_idle()
 
-class MPLFigureEditor(BasicEditorFactory):
+    def _create_canvas(self, parent):
+        """Build a frame holding the MPL canvas and its navigation toolbar."""
+        frame = QtGui.QWidget()
+        mpl_canvas = FigureCanvas(self.value)
+        mpl_canvas.setParent(frame)
+        self._canvas = mpl_canvas
+        mpl_toolbar = NavigationToolbar(mpl_canvas, frame)
 
-   klass = _MPLFigureEditor
+        vbox = QtGui.QVBoxLayout()
+        vbox.addWidget(mpl_canvas)
+        vbox.addWidget(mpl_toolbar)
+        frame.setLayout(vbox)
 
-class MPLInitHandler(Handler):
-    """Handler calls mpl_setup() to initialize mpl events"""
-
-    def init(self, info):
-        """This method gets called after the controls have all been
-        created but before they are displayed.
-        """
-        info.object.mpl_setup()
-        return True
+        return frame
 
-if __name__ == "__main__":
-    # Create a window to demo the editor
-    from traits.api import HasTraits
-    from traitsui.api import View, Item
-    from numpy import sin, cos, linspace, pi
-    from matplotlib.widgets import  RectangleSelector
 
-    class Test(HasTraits):
+class MPLFigureEditor(BasicEditorFactory):
+    """Editor factory: ``Item('figure', editor=MPLFigureEditor())``."""
 
-        figure = Instance(Figure, ())
+    klass = _MPLFigureEditor
 
-        view = View(Item('figure', editor=MPLFigureEditor(),
-                         show_label=False),
-                    handler=MPLInitHandler,
-                    resizable=True)
 
-        def __init__(self):
-            super(Test, self).__init__()
-            self.axes = self.figure.add_subplot(111)
-            t = linspace(0, 2*pi, 200)
-            self.axes.plot(sin(t)*(1+0.5*cos(11*t)), cos(t)*(1+0.5*cos(11*t)))
+class MPLInitHandler(Handler):
+    """Calls ``mpl_setup()`` on the view object once its controls exist.
 
-        def mpl_setup(self):
-            def onselect(eclick, erelease):
-                print("eclick: {}, erelease: {}".format(eclick,erelease))
-
-            self.rs = RectangleSelector(self.axes, onselect,
-                                        drawtype='box',useblit=True)
+    Attach this to a ``View`` when you need to register matplotlib event
+    handlers (pickers, selectors) that require a live canvas.
+    """
 
-    Test().configure_traits()
+    def init(self, info):
+        info.object.mpl_setup()
+        return True

LICENSE

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+MIT License
+
+Copyright (c) 2019 Brendan Griffen
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.