wx.App() should be init'ed in new_figure_manager_given_figure

... not in new_figure_manager.  Otherwise, unpickling a figure fails
with wx if no figure was created previously:
```
$ MPLBACKEND=wxagg python -c 'from pylab import *; plot(); import pickle; pickle.dump(plt.gcf(), open("/tmp/pkl", "wb"))'
$ MPLBACKEND=wxagg python -c 'import pickle; pickle.load(open("/tmp/pkl", "rb"))'
```
fails with "wx._core.PyNoAppError: The wx.App object must be created first!"

Because new_figure_manager calls new_figure_manager_given_figure (see
note in backend_template), it doesn't need to copy the instantiation.

Also note that backend_tk was already doing the init in
new_figure_manager_given_figure.

Author: anntzer

lib/matplotlib/backends/backend_template.py

@@ -158,17 +158,17 @@ def show(*, block=None):
 
 def new_figure_manager(num, *args, FigureClass=Figure, **kwargs):
     """Create a new figure manager instance."""
-    # If a main-level app must be created, this (and
-    # new_figure_manager_given_figure) is the usual place to do it -- see
-    # backend_wx, backend_wxagg and backend_tkagg for examples.  Not all GUIs
-    # require explicit instantiation of a main-level app (e.g., backend_gtk3)
-    # for pylab.
     thisFig = FigureClass(*args, **kwargs)
     return new_figure_manager_given_figure(num, thisFig)
 
 
 def new_figure_manager_given_figure(num, figure):
     """Create a new figure manager instance for the given figure."""
+    # If a main-level app must be created, this is the usual place to do it
+    # -- see the wx and tk backends for examples (the default implementation
+    # of new_figure_manager defers to new_figure_manager_given_figure, so it
+    # also benefits from this instantiation).  Not all GUIs require explicit
+    # instantiation of a main-level app (e.g., backend_gtk3) for pylab.
     canvas = FigureCanvasTemplate(figure)
     manager = FigureManagerTemplate(canvas, num)
     return manager

lib/matplotlib/backends/backend_wx.py

@@ -1356,7 +1356,7 @@ class _BackendWx(_Backend):
     FigureManager = FigureManagerWx
 
     @classmethod
-    def new_figure_manager(cls, num, *args, **kwargs):
+    def new_figure_manager_given_figure(cls, num, figure):
         # Create a wx.App instance if it has not been created so far.
         wxapp = wx.GetApp()
         if wxapp is None:
@@ -1366,10 +1366,6 @@ def new_figure_manager(cls, num, *args, **kwargs):
             # Retain a reference to the app object so that it does not get
             # garbage collected.
             _BackendWx._theWxApp = wxapp
-        return super().new_figure_manager(num, *args, **kwargs)
-
-    @classmethod
-    def new_figure_manager_given_figure(cls, num, figure):
         frame = FigureFrameWx(num, figure, canvas_class=cls.FigureCanvas)
         figmgr = frame.get_figure_manager()
         if mpl.is_interactive():