Deprecate is_pyqt5.

doc/api/api_changes_3.3/deprecations.rst

@@ -535,3 +535,8 @@ These are unused and can be easily reproduced by other date tools.
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The ``cbid`` and ``locator`` attribute are deprecated.  Use
 ``mappable.colorbar_cid`` and ``colorbar.locator``, as for standard colorbars.
+
+``qt_compat.is_pyqt5``
+~~~~~~~~~~~~~~~~~~~~~~
+This function is deprecated in prevision of the future release of PyQt6.  The
+Qt version can be checked using ``QtCore.QT_VERSION_STR``.

examples/user_interfaces/embedding_in_qt_sgskip.py

@@ -14,8 +14,8 @@
 
 import numpy as np
 
-from matplotlib.backends.qt_compat import QtCore, QtWidgets, is_pyqt5
-if is_pyqt5():
+from matplotlib.backends.qt_compat import QtCore, QtWidgets
+if QtCore.QT_VERSION_STR >= "5.":
     from matplotlib.backends.backend_qt5agg import (
         FigureCanvas, NavigationToolbar2QT as NavigationToolbar)
 else:

lib/matplotlib/backends/backend_qt5.py

@@ -105,7 +105,7 @@ def _create_qApp():
         app = QtWidgets.QApplication.instance()
         if app is None:
             # check for DISPLAY env variable on X11 build of Qt
-            if is_pyqt5():
+            if QtCore.QT_VERSION_STR >= "5.":
                 try:
                     importlib.import_module(
                         # i.e. PyQt5.QtX11Extras or PySide2.QtX11Extras.
@@ -130,11 +130,10 @@ def _create_qApp():
         else:
             qApp = app
 
-    if is_pyqt5():
-        try:
-            qApp.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps)
-        except AttributeError:
-            pass
+    try:
+        qApp.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps)
+    except AttributeError:
+        pass
 
 
 def _allow_super_init(__init__):
@@ -332,7 +331,7 @@ def mouseReleaseEvent(self, event):
             FigureCanvasBase.button_release_event(self, x, y, button,
                                                   guiEvent=event)
 
-    if is_pyqt5():
+    if QtCore.QT_VERSION_STR >= "5.":
         def wheelEvent(self, event):
             x, y = self.mouseEventCoords(event)
             # from QWheelEvent::delta doc
@@ -699,7 +698,7 @@ def basedir(self):
         return str(cbook._get_data_path('images'))
 
     def _icon(self, name, color=None):
-        if is_pyqt5():
+        if QtCore.QT_VERSION_STR >= '5.':
             name = name.replace('.png', '_large.png')
         pm = QtGui.QPixmap(str(cbook._get_data_path('images', name)))
         qt_compat._setDevicePixelRatio(pm, qt_compat._devicePixelRatio(self))
@@ -896,9 +895,7 @@ def __init__(self, toolmanager, parent):
 
     @property
     def _icon_extension(self):
-        if is_pyqt5():
-            return '_large.png'
-        return '.png'
+        return '_large.png' if QtCore.QT_VERSION_STR >= '5.' else '.png'
 
     def add_toolitem(
             self, name, group, position, image_file, description, toggle):

lib/matplotlib/backends/qt_compat.py

@@ -85,6 +85,7 @@ def _isdeleted(obj): return not shiboken2.isValid(obj)
         raise ValueError("Unexpected value for the 'backend.qt5' rcparam")
     _getSaveFileName = QtWidgets.QFileDialog.getSaveFileName
 
+    @mpl.cbook.deprecated("3.3", alternative="QtCore.QT_VERSION_STR")
     def is_pyqt5():
         return True
 
@@ -144,6 +145,7 @@ def _isdeleted(obj): return not shiboken.isValid(obj)
         raise ValueError("Unexpected value for the 'backend.qt4' rcparam")
     QtWidgets = QtGui
 
+    @mpl.cbook.deprecated("3.3", alternative="QtCore.QT_VERSION_STR")
     def is_pyqt5():
         return False
 
@@ -183,7 +185,7 @@ def _setDevicePixelRatio(obj, factor): pass
 # These globals are only defined for backcompatibility purposes.
 ETS = dict(pyqt=(QT_API_PYQTv2, 4), pyside=(QT_API_PYSIDE, 4),
            pyqt5=(QT_API_PYQT5, 5), pyside2=(QT_API_PYSIDE2, 5))
-QT_RC_MAJOR_VERSION = 5 if is_pyqt5() else 4
+QT_RC_MAJOR_VERSION = int(QtCore.qVersion().split(".")[0])
 
-if not is_pyqt5():
+if QT_RC_MAJOR_VERSION == 4:
     mpl.cbook.warn_deprecated("3.3", name="support for Qt4")