Fixups from review

efiring · efiring · commit 9e0861e778fd · 2020-09-11T10:01:44.000-10:00
diff --git a/lib/matplotlib/artist.py b/lib/matplotlib/artist.py
@@ -982,7 +982,7 @@ def _set_alpha_for_array(self, alpha):
             Artist.set_alpha(self, alpha)
             return
         alpha = np.asarray(alpha)
-        if not (alpha.min() >= 0 and alpha.max() <= 1):
+        if not (0 <= alpha.min() and alpha.max() <= 1):
             raise ValueError('alpha must be between 0 and 1, inclusive, '
                              f'but min is {alpha.min()}, max is {alpha.max()}')
         self._alpha = alpha
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -837,9 +837,9 @@ def set_alpha(self, alpha):
 
         Parameters
         ----------
-        alpha: float or array of float
+        alpha: float or array of float or None
             If not None, *alpha* values must be between 0 and 1, inclusive.
-            If an array is provided, it's length must match the number of
+            If an array is provided, its length must match the number of
             elements in the collection.  Masked values and nans are not
             supported.
         """
@@ -867,13 +867,13 @@ def update_scalarmappable(self):
             return
         if np.iterable(self._alpha):
             if self._alpha.size != self._A.size:
-                # This can occur with the deprecated behavior of 'flat'
-                # pcolormesh shading.  If we bring the current change in
-                # before that deprecated behavior is removed, we need to
-                # add the explanation to the message below.
                 raise ValueError(f'Data array shape, {self._A.shape} '
                                  'is incompatible with alpha array shape, '
-                                 f'{self._alpha.shape}.')
+                                 f'{self._alpha.shape}. '
+                                 'This can occur with the deprecated '
+                                 'behavior of the "flat" shading option, '
+                                 'in which a row and/or column of the data '
+                                 'array is dropped.')
             # pcolormesh, scatter, maybe others flatten their _A
             self._alpha = self._alpha.reshape(self._A.shape)
 
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -615,8 +615,8 @@ def __call__(self, X, alpha=None, bytes=False):
         if alpha is not None:
             if np.iterable(alpha):
                 alpha = np.asarray(alpha)
-                if not (alpha.shape == xa.shape):
-                    raise ValueError("alpha is array-like but it's shape"
+                if alpha.shape != xa.shape:
+                    raise ValueError("alpha is array-like but its shape"
                                      " %s doesn't match that of X %s" %
                                      (alpha.shape, xa.shape))
 
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
@@ -274,7 +274,7 @@ def set_alpha(self, alpha):
 
         Parameters
         ----------
-        alpha : float or 2-d array or None
+        alpha : float or 2D array-like or None
         """
         martist.Artist._set_alpha_for_array(self, alpha)
         if np.ndim(alpha) not in (0, 2):
