matplotlib · jklymak · Jun 10, 2021 · Jun 10, 2021 · timhoffm · Jun 6, 2021
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -2024,14 +2024,15 @@ def __init__(self, *args, **kwargs):
         kwargs.setdefault("pickradius", 0)
         # end of signature deprecation code
 
-        super().__init__(**kwargs)
         _api.check_shape((None, None, 2), coordinates=coords)
         self._coordinates = coords
         self._antialiased = antialiased
         self._shading = shading
-
         self._bbox = transforms.Bbox.unit()
         self._bbox.update_from_data_xy(self._coordinates.reshape(-1, 2))
+        # super init delayed after own init because array kwarg requires
+        # self._coordinates and self._shading
+        super().__init__(**kwargs)
 
     # Only needed during signature deprecation
     __init__.__signature__ = inspect.signature(
@@ -2047,6 +2048,53 @@ def set_paths(self):
         self._paths = self._convert_mesh_to_paths(self._coordinates)
         self.stale = True
 
+    def set_array(self, A):
         """ 
         Set the value array from array-like *A*. 
         Parameters 
         ---------- 
         A : array-like or None 
             The values that are mapped to colors. 
             The base class `.ScalarMappable` does not make any assumptions on 
             the dimensionality and shape of the value array *A*. 
         """ 
         """ 
         Set the value array from array-like *A*. 
  
         Parameters 
         ---------- 
         A : array-like or None 
             The values that are mapped to colors. 
  
             The base class `.ScalarMappable` does not make any assumptions on 
             the dimensionality and shape of the value array *A*. 
         """ 
+        """
+        Set the data values.
+
+        Parameters
+        ----------
+        A : (M, N) array-like or M*N array-like
+            If the values are provided as a 2D grid, the shape must match the
+            coordinates grid. If the values are 1D, they are reshaped to 2D.
+            M, N follow from the coordinates grid, where the coordinates grid
+            shape is (M, N) for 'gouraud' *shading* and (M+1, N+1) for 'flat'
+            shading.
+        """
+        height, width = self._coordinates.shape[0:-1]
+        misshapen_data = False
+        faulty_data = False
+
+        if self._shading == 'flat':
+            h, w = height-1, width-1
+        else:
+            h, w = height, width
+
+        if A is not None:
+            shape = np.shape(A)
+            if len(shape) == 1:
+                if shape[0] != (h*w):
+                    faulty_data = True
+            elif shape != (h, w):
+                if np.prod(shape) == (h * w):
+                    misshapen_data = True
+                else:
+                    faulty_data = True
+
+            if misshapen_data:
+                _api.warn_deprecated(
+                    "3.5", message=f"For X ({width}) and Y ({height}) "
+                    f"with {self._shading} shading, the expected shape of "
+                    f"A is ({h}, {w}). Passing A ({A.shape}) is deprecated "
+                    "since %(since)s and will become an error %(removal)s.")
+
+            if faulty_data:
+                raise TypeError(
+                    f"Dimensions of A {A.shape} are incompatible with "
+                    f"X ({width}) and/or Y ({height})")
+
+        return super().set_array(A)
+
     def get_datalim(self, transData):
         return (self.get_transform() - transData).transform_bbox(self._bbox)
 

diff --git a/lib/matplotlib/tests/test_collections.py b/lib/matplotlib/tests/test_collections.py
@@ -734,7 +734,7 @@ def test_quadmesh_deprecated_signature(
     X += 0.2 * Y
     coords = np.stack([X, Y], axis=-1)
     assert coords.shape == (3, 4, 2)
-    C = np.linspace(0, 2, 12).reshape(3, 4)
+    C = np.linspace(0, 2, 6).reshape(2, 3)
 
     ax = fig_test.add_subplot()
     ax.set(xlim=(0, 5), ylim=(0, 4))
@@ -789,6 +789,32 @@ def test_quadmesh_deprecated_positional(fig_test, fig_ref):
     ax.add_collection(qmesh)
 
 
+def test_quadmesh_set_array_validation():
+    x = np.arange(11)
+    y = np.arange(8)
+    z = np.random.random((7, 10))
+    fig, ax = plt.subplots()
+    coll = ax.pcolormesh(x, y, z)
+
+    # Test deprecated warning when faulty shape is passed.
+    with pytest.warns(MatplotlibDeprecationWarning):
+        coll.set_array(z.reshape(10, 7))
+
+    z = np.arange(54).reshape((6, 9))
+    with pytest.raises(TypeError, match=r"Dimensions of A \(6, 9\) "
+                       r"are incompatible with X \(11\) and/or Y \(8\)"):
+        coll.set_array(z)
+    with pytest.raises(TypeError, match=r"Dimensions of A \(54,\) "
+                       r"are incompatible with X \(11\) and/or Y \(8\)"):
+        coll.set_array(z.ravel())
+
+    x = np.arange(10)
+    y = np.arange(7)
+    z = np.random.random((7, 10))
+    fig, ax = plt.subplots()
+    coll = ax.pcolormesh(x, y, z, shading='gouraud')
+
+
 def test_quadmesh_get_coordinates():
     x = [0, 1, 2]
     y = [2, 4, 6]
@@ -817,6 +843,19 @@ def test_quadmesh_set_array():
     fig.canvas.draw()
     assert np.array_equal(coll.get_array(), np.ones(9))
 
+    z = np.arange(16).reshape((4, 4))
+    fig, ax = plt.subplots()
+    coll = ax.pcolormesh(x, y, np.ones(z.shape), shading='gouraud')
+    # Test that the collection is able to update with a 2d array
+    coll.set_array(z)
+    fig.canvas.draw()
+    assert np.array_equal(coll.get_array(), z)
+
+    # Check that pre-flattened arrays work too
+    coll.set_array(np.ones(16))
+    fig.canvas.draw()
+    assert np.array_equal(coll.get_array(), np.ones(16))
+
 
 def test_quadmesh_vmin_vmax():
     # test when vmin/vmax on the norm changes, the quadmesh gets updated