Merge pull request #23740 from QuLogic/parentless-mappable

timhoffm · web-flow · commit 86d57976c2e8 · 2022-08-26T08:54:48.000+02:00
Clarify error for colorbar with unparented mappable
diff --git a/doc/api/next_api_changes/removals/22081-AL.rst b/doc/api/next_api_changes/removals/22081-AL.rst
@@ -1,7 +1,10 @@
 colorbar defaults to stealing space from the mappable's axes rather than the current axes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Pass ``ax=plt.gca()`` to restore the previous behavior.
+If the mappable does not have an Axes, then an error will be raised.
+
+Pass the *cax* or *ax* argument to be explicit about where the colorbar will be
+placed. Passing ``ax=plt.gca()`` will restore the previous behavior.
 
 Removal of deprecated ``colorbar`` APIs
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -1245,13 +1245,19 @@ def colorbar(
         """
 
         if ax is None:
-            ax = getattr(mappable, "axes", self.gca())
+            ax = getattr(mappable, "axes", None)
 
         if (self.get_layout_engine() is not None and
                 not self.get_layout_engine().colorbar_gridspec):
             use_gridspec = False
         # Store the value of gca so that we can set it back later on.
         if cax is None:
+            if ax is None:
+                raise ValueError(
+                    'Unable to determine Axes to steal space for Colorbar. '
+                    'Either provide the *cax* argument to use as the Axes for '
+                    'the Colorbar, provide the *ax* argument to steal space '
+                    'from it, or add *mappable* to an Axes.')
             current_ax = self.gca()
             userax = False
             if (use_gridspec and isinstance(ax, SubplotBase)):
diff --git a/lib/matplotlib/tests/test_colorbar.py b/lib/matplotlib/tests/test_colorbar.py
@@ -315,6 +315,14 @@ def test_colorbarbase():
     Colorbar(ax, cmap=plt.cm.bone)
 
 
+def test_parentless_mappable():
+    pc = mpl.collections.PatchCollection([], cmap=plt.get_cmap('viridis'))
+    pc.set_array([])
+
+    with pytest.raises(ValueError, match='Unable to determine Axes to steal'):
+        plt.colorbar(pc)
+
+
 @image_comparison(['colorbar_closed_patch.png'], remove_text=True)
 def test_colorbar_closed_patch():
     # Remove this line when this test image is regenerated.
@@ -675,7 +683,7 @@ def test_colorbar_inverted_ticks():
 def test_mappable_no_alpha():
     fig, ax = plt.subplots()
     sm = cm.ScalarMappable(norm=mcolors.Normalize(), cmap='viridis')
-    fig.colorbar(sm)
+    fig.colorbar(sm, ax=ax)
     sm.set_cmap('plasma')
     plt.draw()
 
