diff --git a/bempp/api/grid/io.py b/bempp/api/grid/io.py
index ace2e75..358eb7d 100644
--- a/bempp/api/grid/io.py
+++ b/bempp/api/grid/io.py
@@ -30,7 +30,7 @@ def import_grid(filename):
     if domain_indices is None or _np.all(domain_indices == 0):
         try:
             domain_indices = mesh.cell_data_dict["gmsh:geometrical"]["triangle"]
-        except:
+        except:  # noqa: E722
             pass
 
     return Grid(vertices, elements, domain_indices=domain_indices)
diff --git a/test/unit/grid/test_grid.py b/test/unit/grid/test_grid.py
index 44597af..fdfca8d 100644
--- a/test/unit/grid/test_grid.py
+++ b/test/unit/grid/test_grid.py
@@ -124,30 +124,39 @@ def test_union_two_grids_one_domain_each(two_element_grid):
     """Test union of two grids, each with one domain."""
 
     two_element_grid_2 = bempp.api.grid.Grid(two_element_grid.vertices, two_element_grid.elements)
-    np.testing.assert_array_equal(bempp.api.grid.union([two_element_grid, two_element_grid_2]).domain_indices, np.array([0 , 0, 1, 1], dtype="uint32"))
+    np.testing.assert_array_equal(
+        bempp.api.grid.union([two_element_grid, two_element_grid_2]).domain_indices,
+        np.array([0 , 0, 1, 1], dtype="uint32"))
 
 
 def test_union_two_grids_two_domains_each(two_element_grid):
     """Test union of two grids, each with two domains."""
 
     two_element_grid = bempp.api.grid.Grid(two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 1])
-    two_element_grid_2 = bempp.api.grid.Grid(two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 1])
-    np.testing.assert_array_equal(bempp.api.grid.union([two_element_grid, two_element_grid_2]).domain_indices, np.array([0, 1, 2, 3], dtype="uint32"))
+    two_element_grid_2 = bempp.api.grid.Grid(
+        two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 1])
+    np.testing.assert_array_equal(
+        bempp.api.grid.union([two_element_grid, two_element_grid_2]).domain_indices,
+        np.array([0, 1, 2, 3], dtype="uint32"))
 
 
 def test_union_two_grids_two_domains_each_unnormalized(two_element_grid):
-    """Test union of two grids, each with two domains,
-    and without domain index normalization."""
+    """Test union of two grids, each with two domains, and without domain index normalization."""
 
     two_element_grid = bempp.api.grid.Grid(two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 2])
-    two_element_grid_2 = bempp.api.grid.Grid(two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 3])
-    np.testing.assert_array_equal(bempp.api.grid.union([two_element_grid, two_element_grid_2], normalize_domain_indices=False).domain_indices, np.array([0, 2, 3, 6], dtype="uint32"))
+    two_element_grid_2 = bempp.api.grid.Grid(
+        two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 3])
+    np.testing.assert_array_equal(
+        bempp.api.grid.union([two_element_grid, two_element_grid_2], normalize_domain_indices=False).domain_indices,
+        np.array([0, 2, 3, 6], dtype="uint32"))
 
 
 def test_union_two_grids_two_domains_each_normalized(two_element_grid):
-    """Test union of two grids, each with two domains,
-    and with domain index normalization."""
+    """Test union of two grids, each with two domains, and with domain index normalization."""
 
     two_element_grid = bempp.api.grid.Grid(two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 2])
-    two_element_grid_2 = bempp.api.grid.Grid(two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 3])
-    np.testing.assert_array_equal(bempp.api.grid.union([two_element_grid, two_element_grid_2], normalize_domain_indices=True).domain_indices, np.array([0, 1, 2, 3], dtype="uint32"))
+    two_element_grid_2 = bempp.api.grid.Grid(
+        two_element_grid.vertices, two_element_grid.elements, domain_indices=[0, 3])
+    np.testing.assert_array_equal(
+        bempp.api.grid.union([two_element_grid, two_element_grid_2], normalize_domain_indices=True).domain_indices,
+        np.array([0, 1, 2, 3], dtype="uint32"))