Fix a few minor contour()-related issues (#2951)

* Check for sane rng in contour filter

* Fix level specification in flying edges example

* Extend contour() scalars type checking

* Make error less confusing by making it less specific

* One more contour example fix

* Check for rng length

* Cover errors with tests

* Cover invalid scalars type check in contour

* Fix the fix in the flying edges example

examples/01-filter/flying_edges.py

@@ -46,7 +46,7 @@ def spider_cage(x, y, z):
 
 # sample and plot
 values = spider_cage(x, y, z)
-mesh = grid.contour(1, values, method='marching_cubes', rng=[1, 0])
+mesh = grid.contour([1], values, method='marching_cubes')
 dist = np.linalg.norm(mesh.points, axis=1)
 mesh.plot(scalars=dist, smooth_shading=True, specular=5, cmap="plasma", show_scalar_bar=False)
 
@@ -88,7 +88,7 @@ def barth_sextic(x, y, z):
 
 # sample and plot
 values = barth_sextic(x, y, z)
-mesh = grid.contour(1, values, method='flying_edges', rng=[-0.0, 0])
+mesh = grid.contour([0], values, method='flying_edges')
 dist = np.linalg.norm(mesh.points, axis=1)
 mesh.plot(scalars=dist, smooth_shading=True, specular=5, cmap="plasma", show_scalar_bar=False)
 
@@ -104,7 +104,7 @@ def angle_to_range(angle):
     return -2 * np.sin(angle)
 
 
-mesh = grid.contour(1, values, method='flying_edges', rng=[angle_to_range(0), 0])
+mesh = grid.contour([angle_to_range(0)], values, method='flying_edges')
 dist = np.linalg.norm(mesh.points, axis=1)
 
 pl = pv.Plotter()
@@ -120,7 +120,7 @@ def angle_to_range(angle):
 pl.open_gif('barth_sextic.gif')
 
 for angle in np.linspace(0, np.pi, 15)[:-1]:
-    new_mesh = grid.contour(1, values, method='flying_edges', rng=[angle_to_range(angle), 0])
+    new_mesh = grid.contour([angle_to_range(angle)], values, method='flying_edges')
     mesh.overwrite(new_mesh)
     pl.update_scalars(np.linalg.norm(new_mesh.points, axis=1), render=False)
     pl.write_frame()

pyvista/core/filters/data_set.py

@@ -1552,6 +1552,15 @@ def contour(
         else:
             raise ValueError(f"Method '{method}' is not supported")
 
+        if rng is not None:
+            if not isinstance(rng, (np.ndarray, collections.abc.Sequence)):
+                raise TypeError(f'Array-like rng expected, got {type(rng).__name__}.')
+            rng_shape = np.shape(rng)
+            if rng_shape != (2,):
+                raise ValueError(f'rng must be a two-length array-like, not {rng}.')
+            if rng[0] > rng[1]:
+                raise ValueError(f'rng must be a sorted min-max pair, not {rng}.')
+
         if isinstance(scalars, str):
             scalars_name = scalars
         elif isinstance(scalars, (collections.abc.Sequence, np.ndarray)):
@@ -1579,9 +1588,7 @@ def contour(
             field = get_array_association(self, scalars_name, preference=preference)
         # NOTE: only point data is allowed? well cells works but seems buggy?
         if field != FieldAssociation.POINT:
-            raise TypeError(
-                f'Contour filter only works on Point data. Array ({scalars}) is in the Cell data.'
-            )
+            raise TypeError('Contour filter only works on point data.')
         alg.SetInputArrayToProcess(
             0,
             0,

tests/test_filters.py

@@ -549,6 +549,12 @@ def test_contour_errors(uniform):
         uniform.contour(method='invalid method')
     with pytest.raises(TypeError, match='Invalid type for `scalars`'):
         uniform.contour(scalars=1)
+    with pytest.raises(TypeError):
+        uniform.contour(rng={})
+    with pytest.raises(ValueError, match='rng must be a two-length'):
+        uniform.contour(rng=[1])
+    with pytest.raises(ValueError, match='rng must be a sorted'):
+        uniform.contour(rng=[2, 1])
 
 
 def test_elevation():