Attach a FigureCanvasBase by default to Figures.

anntzer · anntzer · commit 380c531d58dd · 2018-11-04T10:30:39.000+01:00
This is particularly useful for headless cases, where one just wants to
take advantage of `print_figure`, which is defined on the base class.
For example, one can now do

    for &lt;loop&gt;:
        figure = Figure()
        # do some plotting
        figure.savefig(...)

and let `figure` get gc'd at the next loop iteration; a pyplot-based
solution would instead have to explicitly close() the figure or reuse it
after clf()'ing it.

Also simplifies various places in the codebase where we had to handle
the case of `.canvas = None` previously.
diff --git a/lib/matplotlib/artist.py b/lib/matplotlib/artist.py
@@ -449,9 +449,7 @@ def pickable(self):
         --------
         set_picker, get_picker, pick
         """
-        return (self.figure is not None and
-                self.figure.canvas is not None and
-                self._picker is not None)
+        return self.figure is not None and self._picker is not None
 
     def pick(self, mouseevent):
         """
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -3241,8 +3241,7 @@ def set_xlim(self, left=None, right=None, emit=True, auto=False,
                 if other is not self:
                     other.set_xlim(self.viewLim.intervalx,
                                    emit=False, auto=auto)
-                    if (other.figure != self.figure and
-                            other.figure.canvas is not None):
+                    if other.figure != self.figure:
                         other.figure.canvas.draw_idle()
         self.stale = True
         return left, right
@@ -3630,8 +3629,7 @@ def set_ylim(self, bottom=None, top=None, emit=True, auto=False,
                 if other is not self:
                     other.set_ylim(self.viewLim.intervaly,
                                    emit=False, auto=auto)
-                    if (other.figure != self.figure and
-                            other.figure.canvas is not None):
+                    if other.figure != self.figure:
                         other.figure.canvas.draw_idle()
         self.stale = True
         return bottom, top
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -23,6 +23,7 @@
 
 import matplotlib.artist as martist
 from matplotlib.artist import Artist, allow_rasterization
+from matplotlib.backend_bases import FigureCanvasBase
 import matplotlib.cbook as cbook
 import matplotlib.colorbar as cbar
 import matplotlib.image as mimage
@@ -364,7 +365,7 @@ def __init__(self,
         self._set_artist_props(self.patch)
         self.patch.set_antialiased(False)
 
-        self.canvas = None
+        FigureCanvasBase(self)  # Set self.canvas.
         self._suptitle = None
 
         if subplotpars is None:
@@ -398,8 +399,7 @@ def __init__(self,
     def _repr_html_(self):
         # We can't use "isinstance" here, because then we'd end up importing
         # webagg unconditiionally.
-        if (self.canvas is not None and
-                'WebAgg' in self.canvas.__class__.__name__):
+        if 'WebAgg' in type(self.canvas).__name__:
             from matplotlib.backends import backend_webagg
             return backend_webagg.ipython_inline_display(self)
 
diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -652,8 +652,7 @@ def set_xlim3d(self, left=None, right=None, emit=True, auto=False,
                 if other is not self:
                     other.set_xlim(self.xy_viewLim.intervalx,
                                             emit=False, auto=auto)
-                    if (other.figure != self.figure and
-                        other.figure.canvas is not None):
+                    if other.figure != self.figure:
                         other.figure.canvas.draw_idle()
         self.stale = True
         return left, right
@@ -711,8 +710,7 @@ def set_ylim3d(self, bottom=None, top=None, emit=True, auto=False,
                 if other is not self:
                     other.set_ylim(self.xy_viewLim.intervaly,
                                             emit=False, auto=auto)
-                    if (other.figure != self.figure and
-                        other.figure.canvas is not None):
+                    if other.figure != self.figure:
                         other.figure.canvas.draw_idle()
         self.stale = True
         return bottom, top
@@ -770,8 +768,7 @@ def set_zlim3d(self, bottom=None, top=None, emit=True, auto=False,
                 if other is not self:
                     other.set_zlim(self.zz_viewLim.intervalx,
                                             emit=False, auto=auto)
-                    if (other.figure != self.figure and
-                        other.figure.canvas is not None):
+                    if other.figure != self.figure:
                         other.figure.canvas.draw_idle()
         self.stale = True
         return bottom, top
@@ -1070,17 +1067,14 @@ def mouse_init(self, rotate_btn=1, zoom_btn=3):
 
         """
         self.button_pressed = None
-        canv = self.figure.canvas
-        if canv is not None:
-            c1 = canv.mpl_connect('motion_notify_event', self._on_move)
-            c2 = canv.mpl_connect('button_press_event', self._button_press)
-            c3 = canv.mpl_connect('button_release_event', self._button_release)
-            self._cids = [c1, c2, c3]
-        else:
-            cbook._warn_external("Axes3D.figure.canvas is 'None', mouse "
-                                 "rotation disabled. Set canvas then call "
-                                 "Axes3D.mouse_init().")
-
+        self._cids = [
+            self.figure.canvas.mpl_connect(
+                'motion_notify_event', self._on_move),
+            self.figure.canvas.mpl_connect(
+                'button_press_event', self._button_press),
+            self.figure.canvas.mpl_connect(
+                'button_release_event', self._button_release),
+        ]
         # coerce scalars into array-like, then convert into
         # a regular list to avoid comparisons against None
         # which breaks in recent versions of numpy.
