Default ScalarMappable._A to an empty array instead of None.

anntzer · anntzer · commit 4ed070364f68 · 2018-11-07T18:36:03.000+01:00
This makes it unnecessary for other code to handle None, and is a useful
default for creating "bare" colorbars, which can now be done with the
one-liner

    fig.colorbar(cm.ScalarMappable(norm=norm, cmap=cmap))
diff --git a/lib/matplotlib/cm.py b/lib/matplotlib/cm.py
@@ -210,7 +210,7 @@ def __init__(self, norm=None, cmap=None):
         if norm is None:
             norm = colors.Normalize()
 
-        self._A = None
+        self._A = np.array([])
         #: The Normalization instance of this ScalarMappable.
         self.norm = norm
         #: The Colormap instance of this ScalarMappable.
@@ -360,8 +360,6 @@ def autoscale(self):
         Autoscale the scalar limits on the norm instance using the
         current array
         """
-        if self._A is None:
-            raise TypeError('You must first set_array for mappable')
         self.norm.autoscale(self._A)
         self.changed()
 
@@ -370,8 +368,6 @@ def autoscale_None(self):
         Autoscale the scalar limits on the norm instance using the
         current array, changing only limits that are None
         """
-        if self._A is None:
-            raise TypeError('You must first set_array for mappable')
         self.norm.autoscale_None(self._A)
         self.changed()
 
