Consistent behavior of draw_if_interactive across interactive backends.

Previously it would call `show()` on tk and nbagg, but only
`draw_idle()` on the other backends.  I would guess this was an accident
of history.

Remove that discrepancy, and the customization point
(`trigger_manager_draw`) that I previously implemented to repro
the historical behavior. (`trigger_manager_draw` is in the private
`_Backend` class, so doesn't need a deprecation period.)

Author: anntzer

doc/api/next_api_changes/behavior/18532-AL.rst

@@ -0,0 +1,4 @@
+Consistent behavior of ``draw_if_interactive()`` across backends
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+`.pyplot.draw_if_interactive` no longer shows the window (if it was previously
+unshown) on the tk and nbagg backends, consistently with all other backends.

lib/matplotlib/backend_bases.py

@@ -3514,12 +3514,9 @@ class _Backend:
     # For interactive backends, the `FigureManager` class must be overridden.
     FigureManager = FigureManagerBase
 
-    # The following methods must be left as None for non-interactive backends.
-    # For interactive backends, `trigger_manager_draw` should be a function
-    # taking a manager as argument and triggering a canvas draw, and `mainloop`
-    # should be a function taking no argument and starting the backend main
-    # loop.
-    trigger_manager_draw = None
+    # For interactive backends, `mainloop` should be a function taking no
+    # argument and starting the backend main loop.  It should be left as None
+    # for non-interactive backends.
     mainloop = None
 
     # The following methods will be automatically defined and exported, but
@@ -3543,10 +3540,10 @@ def new_figure_manager_given_figure(cls, num, figure):
 
     @classmethod
     def draw_if_interactive(cls):
-        if cls.trigger_manager_draw is not None and is_interactive():
+        if cls.mainloop is not None and is_interactive():
             manager = Gcf.get_active()
             if manager:
-                cls.trigger_manager_draw(manager)
+                manager.canvas.draw_idle()
 
     @classmethod
     def show(cls, *, block=None):

lib/matplotlib/backends/_backend_tk.py

@@ -883,10 +883,6 @@ def new_figure_manager_given_figure(cls, num, figure):
                 canvas.draw_idle()
             return manager
 
-    @staticmethod
-    def trigger_manager_draw(manager):
-        manager.show()
-
     @staticmethod
     def mainloop():
         managers = Gcf.get_all_fig_managers()

lib/matplotlib/backends/backend_gtk3.py

@@ -942,10 +942,6 @@ class _BackendGTK3(_Backend):
     FigureCanvas = FigureCanvasGTK3
     FigureManager = FigureManagerGTK3
 
-    @staticmethod
-    def trigger_manager_draw(manager):
-        manager.canvas.draw_idle()
-
     @staticmethod
     def mainloop():
         if Gtk.main_level() == 0:

lib/matplotlib/backends/backend_macosx.py

@@ -162,10 +162,6 @@ class _BackendMac(_Backend):
     FigureCanvas = FigureCanvasMac
     FigureManager = FigureManagerMac
 
-    @staticmethod
-    def trigger_manager_draw(manager):
-        manager.canvas.draw_idle()
-
     @staticmethod
     def mainloop():
         _macosx.show()

lib/matplotlib/backends/backend_nbagg.py

@@ -239,10 +239,6 @@ def destroy(event):
         cid = canvas.mpl_connect('close_event', destroy)
         return manager
 
-    @staticmethod
-    def trigger_manager_draw(manager):
-        manager.show()
-
     @staticmethod
     def show(block=None):
         ## TODO: something to do when keyword block==False ?

lib/matplotlib/backends/backend_qt5.py

@@ -1025,10 +1025,6 @@ class _BackendQT5(_Backend):
     FigureCanvas = FigureCanvasQT
     FigureManager = FigureManagerQT
 
-    @staticmethod
-    def trigger_manager_draw(manager):
-        manager.canvas.draw_idle()
-
     @staticmethod
     def mainloop():
         old_signal = signal.getsignal(signal.SIGINT)

lib/matplotlib/backends/backend_webagg.py

@@ -306,10 +306,6 @@ class _BackendWebAgg(_Backend):
     FigureCanvas = FigureCanvasWebAgg
     FigureManager = core.FigureManagerWebAgg
 
-    @staticmethod
-    def trigger_manager_draw(manager):
-        manager.canvas.draw_idle()
-
     @staticmethod
     def show():
         WebAggApplication.initialize()

lib/matplotlib/backends/backend_wx.py

@@ -1649,10 +1649,6 @@ class _BackendWx(_Backend):
     FigureManager = FigureManagerWx
     _frame_class = FigureFrameWx
 
-    @staticmethod
-    def trigger_manager_draw(manager):
-        manager.canvas.draw_idle()
-
     @classmethod
     def new_figure_manager(cls, num, *args, **kwargs):
         # Create a wx.App instance if it has not been created so far.