Merge pull request matplotlib#21301 from anntzer/cmapcall

Simplify `Colormap.__call__` a bit.

Author: jklymak

lib/matplotlib/colors.py

@@ -633,24 +633,20 @@ def __call__(self, X, alpha=None, bytes=False):
         xa[xa < 0] = self._i_under
         xa[mask_bad] = self._i_bad
 
+        lut = self._lut
         if bytes:
-            lut = (self._lut * 255).astype(np.uint8)
-        else:
-            lut = self._lut.copy()  # Don't let alpha modify original _lut.
+            lut = (lut * 255).astype(np.uint8)
 
-        rgba = np.empty(shape=xa.shape + (4,), dtype=lut.dtype)
-        lut.take(xa, axis=0, mode='clip', out=rgba)
+        rgba = lut.take(xa, axis=0, mode='clip')
 
         if alpha is not None:
-            if np.iterable(alpha):
-                alpha = np.asarray(alpha)
-                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))
             alpha = np.clip(alpha, 0, 1)
             if bytes:
-                alpha = (alpha * 255).astype(np.uint8)
+                alpha *= 255  # Will be cast to uint8 upon assignment.
+            if alpha.shape not in [(), xa.shape]:
+                raise ValueError(
+                    f"alpha is array-like but its shape {alpha.shape} does "
+                    f"not match that of X {xa.shape}")
             rgba[..., -1] = alpha
 
             # If the "bad" color is all zeros, then ignore alpha input.