matplotlib · tacaswell · May 15, 2021 · Apr 7, 2021 · Apr 7, 2021 · Apr 7, 2021
diff --git a/doc/api/backend_qt_api.rst b/doc/api/backend_qt_api.rst
@@ -6,16 +6,6 @@ to building the docs.
 .. redirect-from:: /api/backend_qt5agg_api
 .. redirect-from:: /api/backend_qt5cairo_api
 
-:mod:`matplotlib.backends.backend_qt4agg`
-=========================================
-
-.. module:: matplotlib.backends.backend_qt4agg
-
-:mod:`matplotlib.backends.backend_qt4cairo`
-===========================================
-
-.. module:: matplotlib.backends.backend_qt4cairo
-
 :mod:`matplotlib.backends.backend_qt5agg`
 =========================================
 

diff --git a/doc/api/next_api_changes/removals/19894-ES.rst b/doc/api/next_api_changes/removals/19894-ES.rst
@@ -0,0 +1,15 @@
+Qt4-based backends
+~~~~~~~~~~~~~~~~~~
+The qt4agg and qt4cairo backends have been removed. Qt4 has reached its
+end-of-life in 2015 and there are no releases of either PyQt4 or PySide for
+recent versions of Python. Please use one of the Qt5 or Qt6 backends.
+
+``qt_compat.is_pyqt5``
+~~~~~~~~~~~~~~~~~~~~~~
+This function has been removed due to the release of PyQt6. The Qt version can
+be checked using ``QtCore.qVersion()``.
+
+``matplotlib.backends.qt_editor.formsubplottool``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This module has been removed.  Use
+``matplotlib.backends.backend_qt5.SubplotToolQt`` instead.
diff --git a/doc/api/prev_api_changes/api_changes_3.3.0/deprecations.rst b/doc/api/prev_api_changes/api_changes_3.3.0/deprecations.rst
@@ -609,8 +609,8 @@ accepted.
 Qt modifier keys
 ~~~~~~~~~~~~~~~~
 The ``MODIFIER_KEYS``, ``SUPER``, ``ALT``, ``CTRL``, and ``SHIFT``
-global variables of the :mod:`matplotlib.backends.backend_qt4agg`,
-:mod:`matplotlib.backends.backend_qt4cairo`,
+global variables of the ``matplotlib.backends.backend_qt4agg``,
+``matplotlib.backends.backend_qt4cairo``,
 :mod:`matplotlib.backends.backend_qt5agg` and
 :mod:`matplotlib.backends.backend_qt5cairo` modules are deprecated.
 

diff --git a/doc/devel/dependencies.rst b/doc/devel/dependencies.rst
@@ -40,7 +40,6 @@ Matplotlib figures can be rendered to various user interfaces. See
 and the capabilities they provide.
 
 * Tk_ (>= 8.3, != 8.6.0 or 8.6.1) [#]_: for the Tk-based backends.
-* PyQt4_ (>= 4.6) or PySide_ (>= 1.0.3) [#]_: for the Qt4-based backends.
 * PyQt5_ or PySide2_: for the Qt5-based backends.
 * PyGObject_: for the GTK3-based backends [#]_.
 * wxPython_ (>= 4) [#]_: for the wx-based backends.
@@ -49,8 +48,6 @@ and the capabilities they provide.
 * Tornado_: for the WebAgg backend.
 
 .. _Tk: https://docs.python.org/3/library/tk.html
-.. _PyQt4: https://pypi.org/project/PyQt4
-.. _PySide: https://pypi.org/project/PySide
 .. _PyQt5: https://pypi.org/project/PyQt5
 .. _PySide2: https://pypi.org/project/PySide2
 .. _PyGObject: https://pygobject.readthedocs.io/en/latest/

diff --git a/examples/user_interfaces/embedding_in_qt_sgskip.py b/examples/user_interfaces/embedding_in_qt_sgskip.py
@@ -15,12 +15,8 @@
 import numpy as np
 
 from matplotlib.backends.qt_compat import QtCore, QtWidgets
-if QtCore.qVersion() >= "5.":
-    from matplotlib.backends.backend_qt5agg import (
-        FigureCanvas, NavigationToolbar2QT as NavigationToolbar)
-else:
-    from matplotlib.backends.backend_qt4agg import (
-        FigureCanvas, NavigationToolbar2QT as NavigationToolbar)
+from matplotlib.backends.backend_qt5agg import (
+    FigureCanvas, NavigationToolbar2QT as NavigationToolbar)
 from matplotlib.figure import Figure
 
 

diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
@@ -1066,7 +1066,7 @@ def use(backend, *, force=True):
 
         - interactive backends:
           GTK3Agg, GTK3Cairo, MacOSX, nbAgg,
-          Qt4Agg, Qt4Cairo, Qt5Agg, Qt5Cairo,
+          Qt5Agg, Qt5Cairo,
           TkAgg, TkCairo, WebAgg, WX, WXAgg, WXCairo
 
         - non-interactive backends:

diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -99,7 +99,6 @@ def _safe_pyplot_import():
         if current_framework is None:
             raise  # No, something else went wrong, likely with the install...
         backend_mapping = {'qt5': 'qt5agg',
-                           'qt4': 'qt4agg',
                            'gtk3': 'gtk3agg',
                            'wx': 'wxagg',
                            'tk': 'tkagg',
@@ -1680,7 +1679,7 @@ class FigureCanvasBase:
         A high-level figure instance.
     """
 
-    # Set to one of {"qt5", "qt4", "gtk3", "wx", "tk", "macosx"} if an
+    # Set to one of {"qt5", "gtk3", "wx", "tk", "macosx"} if an
     # interactive framework is required, or None otherwise.
     required_interactive_framework = None
 
@@ -1756,7 +1755,7 @@ def _fix_ipython_backend2gui(cls):
             # don't break on our side.
             return
         rif = getattr(cls, "required_interactive_framework", None)
-        backend2gui_rif = {"qt5": "qt", "qt4": "qt", "gtk3": "gtk3",
+        backend2gui_rif = {"qt5": "qt", "gtk3": "gtk3",
                            "wx": "wx", "macosx": "osx"}.get(rif)
         if backend2gui_rif:
             if _is_non_interactive_terminal_ipython(ip):

diff --git a/lib/matplotlib/backends/backend_qt4.py b/lib/matplotlib/backends/backend_qt4.py
diff --git a/lib/matplotlib/backends/backend_qt4agg.py b/lib/matplotlib/backends/backend_qt4agg.py
diff --git a/lib/matplotlib/backends/backend_qt4cairo.py b/lib/matplotlib/backends/backend_qt4cairo.py
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -124,22 +124,22 @@ def _create_qApp():
 
 def _allow_super_init(__init__):
     """
-    Decorator for ``__init__`` to allow ``super().__init__`` on PyQt4/PySide2.
+    Decorator for ``__init__`` to allow ``super().__init__`` on PySide2.
     """
 
     if QT_API == "PyQt5":
 
         return __init__
 
     else:
-        # To work around lack of cooperative inheritance in PyQt4, PySide,
-        # and PySide2, when calling FigureCanvasQT.__init__, we temporarily
-        # patch QWidget.__init__ by a cooperative version, that first calls
+        # To work around lack of cooperative inheritance in PySide2, when
+        # calling FigureCanvasQT.__init__, we temporarily patch
+        # QWidget.__init__ by a cooperative version, that first calls
         # QWidget.__init__ with no additional arguments, and then finds the
         # next class in the MRO with an __init__ that does support cooperative
-        # inheritance (i.e., not defined by the PyQt4, PySide, PySide2, sip
-        # or Shiboken packages), and manually call its `__init__`, once again
-        # passing the additional arguments.
+        # inheritance (i.e., not defined by the PySide2, sip or Shiboken
+        # packages), and manually call its `__init__`, once again passing the
+        # additional arguments.
 
         qwidget_init = QtWidgets.QWidget.__init__
 
@@ -149,7 +149,7 @@ def cooperative_qwidget_init(self, *args, **kwargs):
             next_coop_init = next(
                 cls for cls in mro[mro.index(QtWidgets.QWidget) + 1:]
                 if cls.__module__.split(".")[0] not in [
-                    "PyQt4", "sip", "PySide", "PySide2", "Shiboken"])
+                    "sip", "PySide2", "Shiboken"])
             next_coop_init.__init__(self, *args, **kwargs)
 
         @functools.wraps(__init__)
@@ -293,27 +293,16 @@ def mouseReleaseEvent(self, event):
             FigureCanvasBase.button_release_event(self, x, y, button,
                                                   guiEvent=event)
 
-    if QtCore.qVersion() >= "5.":
-        def wheelEvent(self, event):
-            x, y = self.mouseEventCoords(event)
-            # from QWheelEvent::delta doc
-            if event.pixelDelta().x() == 0 and event.pixelDelta().y() == 0:
-                steps = event.angleDelta().y() / 120
-            else:
-                steps = event.pixelDelta().y()
-            if steps:
-                FigureCanvasBase.scroll_event(
-                    self, x, y, steps, guiEvent=event)
-    else:
-        def wheelEvent(self, event):
-            x = event.x()
-            # flipy so y=0 is bottom of canvas
-            y = self.figure.bbox.height - event.y()
-            # from QWheelEvent::delta doc
-            steps = event.delta() / 120
-            if event.orientation() == QtCore.Qt.Vertical:
-                FigureCanvasBase.scroll_event(
-                    self, x, y, steps, guiEvent=event)
+    def wheelEvent(self, event):
+        x, y = self.mouseEventCoords(event)
+        # from QWheelEvent::delta doc
+        if event.pixelDelta().x() == 0 and event.pixelDelta().y() == 0:
+            steps = event.angleDelta().y() / 120
+        else:
+            steps = event.pixelDelta().y()
+        if steps:
+            FigureCanvasBase.scroll_event(
+                self, x, y, steps, guiEvent=event)
 
     def keyPressEvent(self, event):
         key = self._get_key(event)
@@ -650,8 +639,7 @@ def _icon(self, name):
         Construct a `.QIcon` from an image file *name*, including the extension
         and relative to Matplotlib's "images" data directory.
         """
-        if QtCore.qVersion() >= '5.':
-            name = name.replace('.png', '_large.png')
+        name = name.replace('.png', '_large.png')
         pm = QtGui.QPixmap(str(cbook._get_data_path('images', name)))
         _setDevicePixelRatio(pm, _devicePixelRatioF(self))
         if self.palette().color(self.backgroundRole()).value() < 128: