Streamplot: clean up handling of masks, eliminate warning in test.

The existing test was raising a warning which indicated a problem
in the way a masked color array was being handled.

Author: efiring

lib/matplotlib/streamplot.py

@@ -92,8 +92,7 @@ def streamplot(axes, x, y, u, v, density=1, linewidth=None, color=None,
     if use_multicolor_lines:
         assert color.shape == grid.shape
         line_colors = []
-        if np.any(np.isnan(color)):
-            color = np.ma.array(color, mask=np.isnan(color))
+        color = np.ma.masked_invalid(color)
     else:
         line_kw['color'] = color
         arrow_kw['color'] = color
@@ -112,10 +111,8 @@ def streamplot(axes, x, y, u, v, density=1, linewidth=None, color=None,
     assert u.shape == grid.shape
     assert v.shape == grid.shape
 
-    if np.any(np.isnan(u)):
-        u = np.ma.array(u, mask=np.isnan(u))
-    if np.any(np.isnan(v)):
-        v = np.ma.array(v, mask=np.isnan(v))
+    u = np.ma.masked_invalid(u)
+    v = np.ma.masked_invalid(v)
 
     integrate = get_integrator(u, v, dmap, minlength)
 
@@ -160,7 +157,7 @@ def streamplot(axes, x, y, u, v, density=1, linewidth=None, color=None,
 
         if use_multicolor_lines:
             color_values = interpgrid(color, tgx, tgy)[:-1]
-            line_colors.extend(color_values)
+            line_colors.append(color_values)
             arrow_kw['color'] = cmap(norm(color_values[n]))
 
         p = patches.FancyArrowPatch(arrow_tail,
@@ -174,7 +171,7 @@ def streamplot(axes, x, y, u, v, density=1, linewidth=None, color=None,
                                      transform=transform,
                                      **line_kw)
     if use_multicolor_lines:
-        lc.set_array(np.asarray(line_colors))
+        lc.set_array(np.ma.hstack(line_colors))
         lc.set_cmap(cmap)
         lc.set_norm(norm)
     axes.add_collection(lc)