matplotlib · ivanov · Aug 19, 2019 · Jun 10, 2019
diff --git a/doc/api/next_api_changes/2019-06-12-AL.rst b/doc/api/next_api_changes/2019-06-12-AL.rst
@@ -0,0 +1,11 @@
+API changes
+```````````
+
+The ``required_interactive_framework`` attribute of backend modules introduced
+in Matplotlib 3.0 has been moved to the FigureCanvas class, in order to let it
+be inherited by third-party canvas subclasses and to make it easier to know
+what interactive framework is required by a canvas class.
+
+``backend_qt4.FigureCanvasQT5``, which is an alias for
+``backend_qt5.FigureCanvasQT`` (but only exists under that name in
+``backend_qt4``), has been removed.
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -1560,8 +1560,12 @@ class FigureCanvasBase:
     ----------
     figure : `matplotlib.figure.Figure`
         A high-level figure instance
-
     """
+
+    # Set to one of {"qt5", "qt4", "gtk3", "wx", "tk", "macosx"} if an
+    # interactive framework is required, or None otherwise.
+    required_interactive_framework = None
+
     events = [
         'resize_event',
         'draw_event',
@@ -1633,8 +1637,7 @@ def _fix_ipython_backend2gui(cls):
             # In case we ever move the patch to IPython and remove these APIs,
             # don't break on our side.
             return
-        backend_mod = sys.modules[cls.__module__]
-        rif = getattr(backend_mod, "required_interactive_framework", None)
+        rif = getattr(cls, "required_interactive_framework", None)
         backend2gui_rif = {"qt5": "qt", "qt4": "qt", "gtk3": "gtk3",
                            "wx": "wx", "macosx": "osx"}.get(rif)
         if backend2gui_rif:
@@ -3255,10 +3258,6 @@ class _Backend:
     # class FooBackend(_Backend):
     #     # override the attributes and methods documented below.
 
-    # Set to one of {"qt5", "qt4", "gtk3", "wx", "tk", "macosx"} if an
-    # interactive framework is required, or None otherwise.
-    required_interactive_framework = None
-
     # `backend_version` may be overridden by the subclass.
     backend_version = "unknown"
 
@@ -3341,14 +3340,15 @@ def show(cls, block=None):
 
     @staticmethod
     def export(cls):
-        for name in ["required_interactive_framework",
-                     "backend_version",
-                     "FigureCanvas",
-                     "FigureManager",
-                     "new_figure_manager",
-                     "new_figure_manager_given_figure",
-                     "draw_if_interactive",
-                     "show"]:
+        for name in [
+                "backend_version",
+                "FigureCanvas",
+                "FigureManager",
+                "new_figure_manager",
+                "new_figure_manager_given_figure",
+                "draw_if_interactive",
+                "show",
+        ]:
             setattr(sys.modules[cls.__module__], name, getattr(cls, name))
 
         # For back-compatibility, generate a shim `Show` class.

diff --git a/lib/matplotlib/backends/_backend_tk.py b/lib/matplotlib/backends/_backend_tk.py
@@ -124,6 +124,8 @@ def _on_timer(self):
 
 
 class FigureCanvasTk(FigureCanvasBase):
+    required_interactive_framework = "tk"
+
     keyvald = {65507: 'control',
                65505: 'shift',
                65513: 'alt',
@@ -868,7 +870,6 @@ def trigger(self, *args):
 
 @_Backend.export
 class _BackendTk(_Backend):
-    required_interactive_framework = "tk"
     FigureManager = FigureManagerTk
 
     @classmethod

diff --git a/lib/matplotlib/backends/backend_gtk3.py b/lib/matplotlib/backends/backend_gtk3.py
@@ -97,6 +97,8 @@ def _on_timer(self):
 
 
 class FigureCanvasGTK3(Gtk.DrawingArea, FigureCanvasBase):
+    required_interactive_framework = "gtk3"
+
     keyvald = {65507: 'control',
                65505: 'shift',
                65513: 'alt',
@@ -978,7 +980,6 @@ def error_msg_gtk(msg, parent=None):
 
 @_Backend.export
 class _BackendGTK3(_Backend):
-    required_interactive_framework = "gtk3"
     FigureCanvas = FigureCanvasGTK3
     FigureManager = FigureManagerGTK3
 

diff --git a/lib/matplotlib/backends/backend_macosx.py b/lib/matplotlib/backends/backend_macosx.py
@@ -53,9 +53,10 @@ class FigureCanvasMac(_macosx.FigureCanvas, FigureCanvasAgg):
     ----------
     figure : `matplotlib.figure.Figure`
         A high-level Figure instance
-
     """
 
+    required_interactive_framework = "macosx"
+
     def __init__(self, figure):
         FigureCanvasBase.__init__(self, figure)
         width, height = self.get_width_height()
@@ -172,7 +173,6 @@ def set_message(self, message):
 
 @_Backend.export
 class _BackendMac(_Backend):
-    required_interactive_framework = "macosx"
     FigureCanvas = FigureCanvasMac
     FigureManager = FigureManagerMac
 

diff --git a/lib/matplotlib/backends/backend_qt4.py b/lib/matplotlib/backends/backend_qt4.py
@@ -1,10 +1,11 @@
 from .backend_qt5 import (
     backend_version, SPECIAL_KEYS, SUPER, ALT, CTRL, SHIFT, MODIFIER_KEYS,
-    cursord, _create_qApp, _BackendQT5, TimerQT, MainWindow, FigureManagerQT,
-    NavigationToolbar2QT, SubplotToolQt, error_msg_qt, exception_handler)
-from .backend_qt5 import FigureCanvasQT as FigureCanvasQT5
+    cursord, _create_qApp, _BackendQT5, TimerQT, MainWindow, FigureCanvasQT,
+    FigureManagerQT, NavigationToolbar2QT, SubplotToolQt, error_msg_qt,
+    exception_handler)
 
 
 @_BackendQT5.export
 class _BackendQT4(_BackendQT5):
-    required_interactive_framework = "qt4"
+    class FigureCanvas(FigureCanvasQT):
+        required_interactive_framework = "qt4"
diff --git a/lib/matplotlib/backends/backend_qt4agg.py b/lib/matplotlib/backends/backend_qt4agg.py
@@ -8,4 +8,5 @@
 
 @_BackendQT5Agg.export
 class _BackendQT4Agg(_BackendQT5Agg):
-    required_interactive_framework = "qt4"
+    class FigureCanvas(FigureCanvasQTAgg):
+        required_interactive_framework = "qt4"
diff --git a/lib/matplotlib/backends/backend_qt4cairo.py b/lib/matplotlib/backends/backend_qt4cairo.py
@@ -1,6 +1,7 @@
-from .backend_qt5cairo import _BackendQT5Cairo
+from .backend_qt5cairo import _BackendQT5Cairo, FigureCanvasQTCairo
 
 
 @_BackendQT5Cairo.export
 class _BackendQT4Cairo(_BackendQT5Cairo):
-    required_interactive_framework = "qt4"
+    class FigureCanvas(FigureCanvasQTCairo):
+        required_interactive_framework = "qt4"
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -211,6 +211,7 @@ def _timer_stop(self):
 
 
 class FigureCanvasQT(QtWidgets.QWidget, FigureCanvasBase):
+    required_interactive_framework = "qt5"
 
     # map Qt button codes to MouseEvent's ones:
     buttond = {QtCore.Qt.LeftButton: MouseButton.LEFT,
@@ -1029,7 +1030,6 @@ def trigger(self, *args, **kwargs):
 
 @_Backend.export
 class _BackendQT5(_Backend):
-    required_interactive_framework = "qt5"
     FigureCanvas = FigureCanvasQT
     FigureManager = FigureManagerQT
 

diff --git a/lib/matplotlib/backends/backend_wx.py b/lib/matplotlib/backends/backend_wx.py
@@ -519,6 +519,8 @@ class _FigureCanvasWxBase(FigureCanvasBase, wx.Panel):
     we give a hint as to our preferred minimum size.
     """
 
+    required_interactive_framework = "wx"
+
     keyvald = {
         wx.WXK_CONTROL: 'control',
         wx.WXK_SHIFT: 'shift',
@@ -1933,7 +1935,6 @@ def OnPrintPage(self, page):
 
 @_Backend.export
 class _BackendWx(_Backend):
-    required_interactive_framework = "wx"
     FigureCanvas = FigureCanvasWx
     FigureManager = FigureManagerWx
     _frame_class = FigureFrameWx

diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
@@ -224,7 +224,8 @@ def switch_backend(newbackend):
     _log.debug("Loaded backend %s version %s.",
                newbackend, Backend.backend_version)
 
-    required_framework = Backend.required_interactive_framework
+    required_framework = getattr(
+        Backend.FigureCanvas, "required_interactive_framework", None)
     if required_framework is not None:
         current_framework = \
             matplotlib.backends._get_running_interactive_framework()