Added and tested proper exception handling concerning array shape

skimage/measure/_ccomp.pyx

@@ -45,9 +45,7 @@ ctypedef struct bginfo:
     DTYPE_t background_label
 
 
-cdef bginfo get_bginfo(background_val):
-    cdef bginfo ret
-
+cdef void get_bginfo(background_val, bginfo *ret) except *:
     if background_val is None:
         warnings.warn(DeprecationWarning(
                 'The default value for `background` will change to 0 in v0.12'
@@ -60,7 +58,6 @@ cdef bginfo get_bginfo(background_val):
     # upon the first background pixel occurence
     ret.background_node = -999
     ret.background_label = -1
-    return ret
 
 
 # A pixel has neighbors that have already been scanned.
@@ -110,13 +107,11 @@ cdef struct s_shpinfo:
     fun_ravel ravel_index
 
 
-cdef shape_info get_shape_info(inarr_shape):
+cdef void get_shape_info(inarr_shape, shape_info *res) except *:
     """
     Precalculates all the needed data from the input array shape
     and stores them in the shape_info struct.
     """
-    cdef shape_info res
-
     res.y = 1
     res.z = 1
     res.ravel_index = ravel_index2D
@@ -135,7 +130,9 @@ cdef shape_info get_shape_info(inarr_shape):
         res.z = inarr_shape[0]
         res.ravel_index = ravel_index3D
     else:
-        assert "Only for images of dimension 1-3 (got %s)" % res.ndim
+        raise NotImplementedError(
+            "Only for images of dimension 1-3 are supported, got a %sD one"
+            % res.ndim)
 
     res.numels = res.x * res.y * res.z
 
@@ -152,12 +149,12 @@ cdef shape_info get_shape_info(inarr_shape):
     # res.DEX[D_ee] = 0
 
     # So now the 2nd (needed for 2D and 3D) part, y = 0, z = 1
-    res.DEX[D_ea] = res.ravel_index(-1, -1, 0, & res)
+    res.DEX[D_ea] = res.ravel_index(-1, -1, 0, res)
     res.DEX[D_eb] = res.DEX[D_ea] + 1
     res.DEX[D_ec] = res.DEX[D_eb] + 1
 
     # And now the 3rd (needed only for 3D) part, z = 0
-    res.DEX[D_ef] = res.ravel_index(-1, -1, -1, & res)
+    res.DEX[D_ef] = res.ravel_index(-1, -1, -1, res)
     res.DEX[D_eg] = res.DEX[D_ef] + 1
     res.DEX[D_eh] = res.DEX[D_ef] + 2
     res.DEX[D_ei] = res.DEX[D_ef] - res.DEX[D_eb]  # DEX[D_eb] = one row up, remember?
@@ -167,8 +164,6 @@ cdef shape_info get_shape_info(inarr_shape):
     res.DEX[D_em] = res.DEX[D_el] + 1
     res.DEX[D_en] = res.DEX[D_el] + 2
 
-    return res
-
 
 cdef inline void join_trees_wrapper(DTYPE_t *data_p, DTYPE_t *forest_p,
                                     DTYPE_t rindex, INTS_t idxdiff):
@@ -354,19 +349,14 @@ def label(input, DTYPE_t neighbors=8, background=None, return_num=False):
     cdef shape_info shapeinfo
     cdef bginfo bg
 
-    shapeinfo = get_shape_info(input.shape)
-    bg = get_bginfo(background)
+    get_shape_info(input.shape, &shapeinfo)
+    get_bginfo(background, &bg)
 
     if neighbors != 4 and neighbors != 8:
         raise ValueError('Neighbors must be either 4 or 8.')
 
     scanBG(data_p, forest_p, & shapeinfo, & bg)
-    if shapeinfo.ndim == 1:
-        scan1D(data_p, forest_p, & shapeinfo, & bg, neighbors, 0, 0)
-    elif shapeinfo.ndim == 2:
-        scan2D(data_p, forest_p, & shapeinfo, & bg, neighbors, 0)
-    elif shapeinfo.ndim == 3:
-        scan3D(data_p, forest_p, & shapeinfo, & bg, neighbors)
+    scan3D(data_p, forest_p, & shapeinfo, & bg, neighbors)
 
     # Label output
     cdef DTYPE_t ctr

skimage/morphology/tests/test_ccomp.py

@@ -244,6 +244,10 @@ class TestConnectedComponents3d:
 
         assert_array_equal(label(x, background=0, return_num=True)[1], 3)
 
+    def test_nd(self):
+        x = np.ones((1, 2, 3, 4))
+        np.testing.assert_raises(NotImplementedError, label, x)
+
 
 if __name__ == "__main__":
     run_module_suite()