Add comment and test for _pcolorargs

Author: efiring

lib/matplotlib/axes.py

@@ -7316,13 +7316,33 @@ def imshow(self, X, cmap=None, norm=None, aspect=None,
 
         return im
 
-    def _pcolorargs(self, funcname, *args, **kw):
+    @staticmethod
+    def _pcolorargs(funcname, *args, **kw):
+        # This takes one kwarg, allmatch.
+        # If allmatch is True, then the incoming X, Y, C must
+        # have matching dimensions, taking into account that
+        # X and Y can be 1-D rather than 2-D.  This perfect
+        # match is required for Gouroud shading.  For flat
+        # shading, X and Y specify boundaries, so we need
+        # one more boundary than color in each direction.
+        # For convenience, and consistent with Matlab, we
+        # discard the last row and/or column of C if necessary
+        # to meet this condition.  This is done if allmatch
+        # is False.
+
         allmatch = kw.pop("allmatch", False)
+
         if len(args) == 1:
             C = args[0]
             numRows, numCols = C.shape
-            X, Y = np.meshgrid(np.arange(numCols + 1), np.arange(numRows + 1))
-        elif len(args) == 3:
+            if allmatch:
+                X, Y = np.meshgrid(np.arange(numCols), np.arange(numRows))
+            else:
+                X, Y = np.meshgrid(np.arange(numCols + 1),
+                                   np.arange(numRows + 1))
+            return X, Y, C
+
+        if len(args) == 3:
             X, Y, C = args
             numRows, numCols = C.shape
         else:

lib/matplotlib/tests/test_axes.py

@@ -1,4 +1,6 @@
 from nose.tools import assert_equal
+from nose.tools import assert_raises
+
 import numpy as np
 from numpy import ma
 
@@ -293,7 +295,6 @@ def test_shaped_data():
     plt.plot( y2 )
 
     plt.subplot( 413 )
-    from nose.tools import assert_raises
     assert_raises(ValueError,plt.plot, (y1,y2))
 
     plt.subplot( 414 )
@@ -662,6 +663,20 @@ def test_pcolormesh():
     ax = fig.add_subplot(133)
     ax.pcolormesh(Qx,Qz,Z, shading="gouraud")
 
+def test_pcolorargs():
+    n = 12
+    x = np.linspace(-1.5, 1.5, n)
+    y = np.linspace(-1.5, 1.5, n*2)
+    X, Y = np.meshgrid(x, y)
+    Z = np.sqrt(X**2 + Y**2)/5
+
+    _, ax = plt.subplots()
+    assert_raises(TypeError, ax.pcolormesh, y, x, Z)
+    assert_raises(TypeError, ax.pcolormesh, X, Y, Z.T)
+    assert_raises(TypeError, ax.pcolormesh, x, y, Z[:-1, :-1],
+                  shading="gouraud")
+    assert_raises(TypeError, ax.pcolormesh, X, Y, Z[:-1, :-1],
+                  shading="gouraud")
 
 @image_comparison(baseline_images=['canonical'])
 def test_canonical():