Make figure parameter optional when constructing canvases.

Auto-instantiating a Figure seems reasonable enough, and helps with GUI
builders.  (The auto-instantiated figure must be a plain Figure(), not
a a pyplot-registered figure, both because most likely one should not
use pyplot when building GUIs, and also more prosaically because that
would run into a circular dependency (pyplot needs a canvas already
instantiated (actually a manager that holds a canvas) to store into its
global registry).

Author: anntzer

lib/matplotlib/backend_bases.py

@@ -1709,10 +1709,13 @@ def supports_blit(cls):
         return (hasattr(cls, "copy_from_bbox")
                 and hasattr(cls, "restore_region"))
 
-    def __init__(self, figure):
+    def __init__(self, figure=None):
+        from matplotlib.figure import Figure
         self._fix_ipython_backend2gui()
         self._is_idle_drawing = True
         self._is_saving = False
+        if figure is None:
+            figure = Figure()
         figure.set_canvas(self)
         self.figure = figure
         self.manager = None

lib/matplotlib/backends/_backend_tk.py

@@ -162,7 +162,7 @@ class FigureCanvasTk(FigureCanvasBase):
     @_api.delete_parameter(
         "3.4", "resize_callback",
         alternative="get_tk_widget().bind('<Configure>', ..., True)")
-    def __init__(self, figure, master=None, resize_callback=None):
+    def __init__(self, figure=None, master=None, resize_callback=None):
         super().__init__(figure)
         self._idle = True
         self._idle_callback = None

lib/matplotlib/backends/backend_gtk3.py

@@ -102,7 +102,7 @@ class FigureCanvasGTK3(Gtk.DrawingArea, FigureCanvasBase):
                   | Gdk.EventMask.POINTER_MOTION_HINT_MASK
                   | Gdk.EventMask.SCROLL_MASK)
 
-    def __init__(self, figure):
+    def __init__(self, figure=None):
         FigureCanvasBase.__init__(self, figure)
         GObject.GObject.__init__(self)
 

lib/matplotlib/backends/backend_qt5.py

@@ -206,13 +206,13 @@ class FigureCanvasQT(QtWidgets.QWidget, FigureCanvasBase):
                }
 
     @_allow_super_init
-    def __init__(self, figure):
+    def __init__(self, figure=None):
         _create_qApp()
         super().__init__(figure=figure)
 
         # We don't want to scale up the figure DPI more than once.
         # Note, we don't handle a signal for changing DPI yet.
-        figure._original_dpi = figure.dpi
+        self.figure._original_dpi = self.figure.dpi
         self._update_figure_dpi()
         # In cases with mixed resolution displays, we need to be careful if the
         # dpi_ratio changes - in this case we need to resize the canvas

lib/matplotlib/backends/backend_qt5agg.py

@@ -16,7 +16,7 @@
 
 class FigureCanvasQTAgg(FigureCanvasAgg, FigureCanvasQT):
 
-    def __init__(self, figure):
+    def __init__(self, figure=None):
         # Must pass 'figure' as kwarg to Qt base class.
         super().__init__(figure=figure)
 

lib/matplotlib/backends/backend_qt5cairo.py

@@ -6,7 +6,7 @@
 
 
 class FigureCanvasQTCairo(FigureCanvasQT, FigureCanvasCairo):
-    def __init__(self, figure):
+    def __init__(self, figure=None):
         super().__init__(figure=figure)
         self._renderer = RendererCairo(self.figure.dpi)
         self._renderer.set_width_height(-1, -1)  # Invalid values.

lib/matplotlib/backends/backend_wx.py

@@ -494,7 +494,7 @@ class _FigureCanvasWxBase(FigureCanvasBase, wx.Panel):
         wx.WXK_NUMPAD_DELETE: 'delete',
     }
 
-    def __init__(self, parent, id, figure):
+    def __init__(self, parent, id, figure=None):
         """
         Initialize a FigureWx instance.
 
@@ -504,7 +504,7 @@ def __init__(self, parent, id, figure):
         """
 
         FigureCanvasBase.__init__(self, figure)
-        w, h = map(math.ceil, figure.bbox.size)
+        w, h = map(math.ceil, self.figure.bbox.size)
         # Set preferred window size hint - helps the sizer, if one is connected
         wx.Panel.__init__(self, parent, id, size=wx.Size(w, h))
         # Create the drawing bitmap

lib/matplotlib/tests/test_backend_bases.py

@@ -5,9 +5,11 @@
     NavigationToolbar2, RendererBase)
 from matplotlib.backend_tools import (ToolZoom, ToolPan, RubberbandBase,
                                       ToolViewsPositions, _views_positions)
+from matplotlib.figure import Figure
 import matplotlib.pyplot as plt
 import matplotlib.transforms as transforms
 import matplotlib.path as path
+
 import numpy as np
 import pytest
 
@@ -53,6 +55,10 @@ def check(master_transform, paths, all_transforms,
     check(id, paths, tforms_matrices, offsets, facecolors[0:1], edgecolors)
 
 
+def test_canvas_ctor():
+    assert isinstance(FigureCanvasBase().figure, Figure)
+
+
 def test_get_default_filename(tmpdir):
     plt.rcParams['savefig.directory'] = str(tmpdir)
     fig = plt.figure()