From b316d4b20e5d967fb2c8891b7e0fbb2b3b7f7ce5 Mon Sep 17 00:00:00 2001
From: Antony Lee <anntzer.lee@gmail.com>
Date: Thu, 15 Oct 2020 22:07:51 +0200
Subject: [PATCH] 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).
---
 lib/matplotlib/backend_bases.py             | 5 ++++-
 lib/matplotlib/backends/_backend_tk.py      | 2 +-
 lib/matplotlib/backends/backend_gtk3.py     | 2 +-
 lib/matplotlib/backends/backend_qt5.py      | 4 ++--
 lib/matplotlib/backends/backend_qt5agg.py   | 2 +-
 lib/matplotlib/backends/backend_qt5cairo.py | 2 +-
 lib/matplotlib/backends/backend_wx.py       | 4 ++--
 lib/matplotlib/tests/test_backend_bases.py  | 6 ++++++
 8 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
index 99db4957b277..0bb1db9f97ba 100644
--- a/lib/matplotlib/backend_bases.py
+++ b/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
diff --git a/lib/matplotlib/backends/_backend_tk.py b/lib/matplotlib/backends/_backend_tk.py
index 992e2a7b7eb1..8a541adbe29e 100644
--- a/lib/matplotlib/backends/_backend_tk.py
+++ b/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
diff --git a/lib/matplotlib/backends/backend_gtk3.py b/lib/matplotlib/backends/backend_gtk3.py
index 4c63505352c2..68e43ca2b32b 100644
--- a/lib/matplotlib/backends/backend_gtk3.py
+++ b/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)
 
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
index 4a63e79d220b..afb2bcb483e8 100644
--- a/lib/matplotlib/backends/backend_qt5.py
+++ b/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
diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
index 90eafca5334d..897c28c38f04 100644
--- a/lib/matplotlib/backends/backend_qt5agg.py
+++ b/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)
 
diff --git a/lib/matplotlib/backends/backend_qt5cairo.py b/lib/matplotlib/backends/backend_qt5cairo.py
index a375d1f4d1e2..4b6d7305e7c1 100644
--- a/lib/matplotlib/backends/backend_qt5cairo.py
+++ b/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.
diff --git a/lib/matplotlib/backends/backend_wx.py b/lib/matplotlib/backends/backend_wx.py
index a5f335cbbc32..421601039fc9 100644
--- a/lib/matplotlib/backends/backend_wx.py
+++ b/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
diff --git a/lib/matplotlib/tests/test_backend_bases.py b/lib/matplotlib/tests/test_backend_bases.py
index 25183f7a06e2..7ca260c187ef 100644
--- a/lib/matplotlib/tests/test_backend_bases.py
+++ b/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()

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