Add a Figure._get_cachedRenderer() method

dstansby · dstansby · commit 64fc6fbf26ff · 2021-10-23T11:50:29.000+01:00
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -2376,6 +2376,13 @@ def axes(self):
 
     get_axes = axes.fget
 
+    def _get_cachedRenderer(self, error_if_none=True):
+        # Get the cached renderer, raising an error if it doesn't exist yet
+        if error_if_none and self._cachedRenderer is None:
+            raise RuntimeError("This code can only be used after an "
+                               "initial draw which caches the renderer.")
+        return self._cachedRenderer
+
     def _get_dpi(self):
         return self._dpi
 
@@ -2829,10 +2836,7 @@ def draw_artist(self, a):
         This method can only be used after an initial draw of the figure,
         because that creates and caches the renderer needed here.
         """
-        if self._cachedRenderer is None:
-            raise AttributeError("draw_artist can only be used after an "
-                                 "initial draw which caches the renderer")
-        a.draw(self._cachedRenderer)
+        a.draw(self._get_cachedRenderer())
 
     def __getstate__(self):
         state = super().__getstate__()
diff --git a/lib/matplotlib/legend.py b/lib/matplotlib/legend.py
@@ -881,7 +881,7 @@ def get_title(self):
     def get_window_extent(self, renderer=None):
         # docstring inherited
         if renderer is None:
-            renderer = self.figure._cachedRenderer
+            renderer = self.figure._get_cachedRenderer()
         return self._legend_box.get_window_extent(renderer=renderer)
 
     def get_tightbbox(self, renderer):
diff --git a/lib/matplotlib/tests/test_legend.py b/lib/matplotlib/tests/test_legend.py
@@ -880,3 +880,11 @@ def test_subfigure_legend():
     ax.plot([0, 1], [0, 1], label="line")
     leg = subfig.legend()
     assert leg.figure is subfig
+
+
+def test_no_renderer_error():
+    leg = plt.legend()
+    with pytest.raises(
+            RuntimeError,
+            match='This code can only be used after an initial draw'):
+        leg.get_window_extent()
