fix mypy errors

meshmode/mesh/processing.py

@@ -21,7 +21,6 @@
 """
 
 from functools import reduce
-from numbers import Real
 from typing import Optional, Union, Any, Tuple, Dict, List, Set, Sequence
 
 from dataclasses import dataclass
@@ -151,9 +150,10 @@ def _filter_mesh_groups(
     # {{{ filter vertex indices
 
     filtered_vertex_indices = [
-            mesh.groups[igrp].vertex_indices[
+            grp.vertex_indices[
                     filtered_group_elements[igrp], :]
-            for igrp in range(len(mesh.groups))]
+            for igrp, grp in enumerate(mesh.groups)
+            if grp.vertex_indices is not None]
 
     filtered_vertex_indices_flat = np.concatenate([indices.ravel() for indices
                 in filtered_vertex_indices])
@@ -1322,14 +1322,14 @@ def map_mesh(mesh, f):  # noqa
 # {{{ affine map
 
 def affine_map(mesh,
-        A: Optional[Union[Real, np.ndarray]] = None,    # noqa: N803
-        b: Optional[Union[Real, np.ndarray]] = None):
+        A: Optional[Union[np.generic, np.ndarray]] = None,    # noqa: N803
+        b: Optional[Union[np.generic, np.ndarray]] = None):
     """Apply the affine map :math:`f(x) = A x + b` to the geometry of *mesh*."""
 
-    if isinstance(A, Real):
+    if isinstance(A, np.generic):
         A = np.diag([A] * mesh.ambient_dim)             # noqa: N806
 
-    if isinstance(b, Real):
+    if isinstance(b, np.generic):
         b = np.array([b] * mesh.ambient_dim)
 
     if A is None and b is None:
@@ -1432,7 +1432,7 @@ def _get_rotation_matrix_from_angle_and_axis(theta, axis):
 
 
 def rotate_mesh_around_axis(mesh, *,
-        theta: Real,
+        theta: np.generic,
         axis: Optional[np.ndarray] = None):
     """Rotate the mesh by *theta* radians around the axis *axis*.