Reduce object-oriented boilerplate for users

Now, one can work with the default backend to create figures, without
the need to attach a canvas manually. For example:

import matplotlib
matplotlib.use('agg')
from matplotlib.figure import Figure

fig = Figure()
ax = fig.add_subplot(1, 1, 1)
ax.plot([1, 2, 3], [1, 2, 3])
fig.savefig('oo.png')

Author: dmcdougall

lib/matplotlib/figure.py

@@ -318,7 +318,7 @@ def __init__(self,
         self.patch.set_aa(False)
 
         self._hold = rcParams['axes.hold']
-        self.canvas = None
+        self.canvas = self._current_figure_canvas()
 
         if subplotpars is None:
             subplotpars = SubplotParams()
@@ -330,6 +330,48 @@ def __init__(self,
         self.clf()
         self._cachedRenderer = None
 
+    def _current_figure_canvas(self):
+        b = rcParams['backend'].lower()
+        if b == 'agg':
+            from backends.backend_agg import FigureCanvasAgg as FigureCanvas
+        elif b == 'cairo':
+            from backends.backend_cairo import FigureCanvasCairo as FigureCanvas
+        elif b == 'cocoaag':
+            from backends.backend_cocoaagg import FigureCanvasCocoaAgg as FigureCanvas
+        elif b == 'fltkagg':
+            from backends.backend_fltkagg import FigureCanvasFltkAgg as FigureCanvas
+        elif b == 'gdk':
+            from backends.backend_gdk import FigureCanvasGDK as FigureCanvas
+        elif b == 'gtk':
+            from backends.backend_gtk import FigureCanvasGTK as FigureCanvas
+        elif b == 'gtkagg':
+            from backends.backend_gtkagg import FigureCanvasGTKAgg as FigureCanvas
+        elif b == 'gtkcairo':
+            from backends.backend_gtkcairo import FigureCanvasGTKCairo as FigureCanvas
+        elif b == 'macosx':
+            from backends.backend_macosx import FigureCanvasMac as FigureCanvas
+        elif b == 'pdf':
+            from backends.backend_pdf import FigureCanvasPdf as FigureCanvas
+        elif b == 'ps':
+            from backends.backend_ps import FigureCanvasPS as FigureCanvas
+        elif b == 'qtagg':
+            from backends.backend_qtagg import FigureCanvasQTAgg as FigureCanvas
+        elif b == 'qt4agg':
+            from backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
+        elif b == 'svg':
+            from backends.backend_svg import FigureCanvasSVG as FigureCanvas
+        elif b == 'template':
+            from backends.backend_template import FigureCanvasTemplate as FigureCanvas
+        elif b == 'tkagg':
+            from backends.backend_tkagg import FigureCanvasTkAgg as FigureCanvas
+        elif b == 'wx':
+            from backends.backend_wx import FigureCanvasWx as FigureCanvas
+        elif b == 'wxagg':
+            from backends.backend_wxagg import FigureCanvasWxAgg as FigureCanvas
+        else:
+            return None
+        return FigureCanvas(self)
+
     def _get_axes(self):
         return self._axstack.as_list()