diff --git a/examples/advection/surface.py b/examples/advection/surface.py
index c7b96c69044df5996903b891c92a7270dec0b788..8eca7ab43755b293c2a50388b438747d17c4fb83 100644
--- a/examples/advection/surface.py
+++ b/examples/advection/surface.py
@@ -222,7 +222,7 @@ def main(ctx_factory, dim=2, order=4, use_quad=False, visualize=False):
     step = 0
 
     event = dt_stepper.StateComputed(0.0, 0, 0, u0)
-    plot(event, "fld-surface-%04d" % 0)
+    plot(event, f"fld-surface-{0:04d}")
 
     if visualize and dim == 3:
         from grudge.shortcuts import make_visualizer
@@ -253,7 +253,7 @@ def main(ctx_factory, dim=2, order=4, use_quad=False, visualize=False):
         step += 1
         if step % 10 == 0:
             norm_u = actx.to_numpy(op.norm(dcoll, event.state_component, 2))
-            plot(event, "fld-surface-%04d" % step)
+            plot(event, f"fld-surface-{step:04d}")
 
         logger.info("[%04d] t = %.5f |u| = %.5e", step, event.t, norm_u)
 
diff --git a/examples/advection/var-velocity.py b/examples/advection/var-velocity.py
index 7b6cebd8318868b5bff9453760422a5ff7ef8343..753bf263dc437e4c9bea332d1885fda066ab3f4e 100644
--- a/examples/advection/var-velocity.py
+++ b/examples/advection/var-velocity.py
@@ -211,7 +211,7 @@ def main(ctx_factory, dim=2, order=4, use_quad=False, visualize=False,
 
         if step % 10 == 0:
             norm_u = actx.to_numpy(op.norm(dcoll, event.state_component, 2))
-            plot(event, "fld-var-velocity-%04d" % step)
+            plot(event, f"fld-var-velocity-{step:04d}")
 
             logger.info("[%04d] t = %.5f |u| = %.5e", step, event.t, norm_u)
             # NOTE: These are here to ensure the solution is bounded for the
diff --git a/examples/advection/weak.py b/examples/advection/weak.py
index 35ef9bf8eb4254ad2dee96d9e503b75989e0742f..72a2932d0dcdeb9fc0c48db00bc9b84c288291e2 100644
--- a/examples/advection/weak.py
+++ b/examples/advection/weak.py
@@ -184,7 +184,7 @@ def main(ctx_factory, dim=2, order=4, visualize=False):
 
         if step % 10 == 0:
             norm_u = actx.to_numpy(op.norm(dcoll, event.state_component, 2))
-            plot(event, "fld-weak-%04d" % step)
+            plot(event, f"fld-weak-{step:04d}")
 
         step += 1
         logger.info("[%04d] t = %.5f |u| = %.5e", step, event.t, norm_u)
diff --git a/grudge/geometry/metrics.py b/grudge/geometry/metrics.py
index e1fbe8f47092ef32601a6a13b2db39d2c1e41991..67fd19bbb008a53227a0f72af095ba13155eb247 100644
--- a/grudge/geometry/metrics.py
+++ b/grudge/geometry/metrics.py
@@ -837,7 +837,7 @@ def second_fundamental_form(
     elif dim == 2:
         second_ref_axes = [((0, 2),), ((0, 1), (1, 1)), ((1, 2),)]
     else:
-        raise ValueError("%dD surfaces not supported" % dim)
+        raise ValueError(f"{dim}D surfaces not supported")
 
     from pytools import flatten
 
diff --git a/grudge/op.py b/grudge/op.py
index f9e762f14a2af1902d8d0d1740cfdd3e8aea19b5..468024e449f4d493683163c347c5d203fcc061fb 100644
--- a/grudge/op.py
+++ b/grudge/op.py
@@ -217,8 +217,9 @@ def _gradient_kernel(actx, out_discr, in_discr, get_diff_mat, inv_jac_mat, vec,
             inv_jac_mat)]
 
     return make_obj_array([
-            DOFArray(
-                actx, data=tuple([pgg_i[xyz_axis] for pgg_i in per_group_grads]))
+            DOFArray(actx, data=tuple([  # noqa: C409
+                pgg_i[xyz_axis] for pgg_i in per_group_grads
+                ]))
             for xyz_axis in range(out_discr.ambient_dim)])
 
 
diff --git a/test/test_grudge.py b/test/test_grudge.py
index 8a5a5a67852f35a719cceafe7b1f503ae1c5a018..b0849310b7b91c3fa359be0d67435825916e53c2 100644
--- a/test/test_grudge.py
+++ b/test/test_grudge.py
@@ -784,7 +784,7 @@ def test_convergence_advec(actx_factory, mesh_name, mesh_pars, op_type, flux_typ
             elif dim == 3:
                 dt_factor = 2
             else:
-                raise ValueError("dt_factor not known for %dd" % dim)
+                raise ValueError(f"dt_factor not known for {dim}d")
         elif mesh_name.startswith("warped"):
             dim = int(mesh_name[-1:])
             mesh = mgen.generate_warped_rect_mesh(dim, order=order,
@@ -795,7 +795,7 @@ def test_convergence_advec(actx_factory, mesh_name, mesh_pars, op_type, flux_typ
             elif dim == 3:
                 dt_factor = 2
             else:
-                raise ValueError("dt_factor not known for %dd" % dim)
+                raise ValueError(f"dt_factor not known for {dim}d")
         else:
             raise ValueError("invalid mesh name: " + mesh_name)
 
@@ -861,7 +861,7 @@ def test_convergence_advec(actx_factory, mesh_name, mesh_pars, op_type, flux_typ
 
             if visualize:
                 vis.write_vtk_file(
-                    "fld-%s-%04d.vtu" % (mesh_par, step),
+                    f"fld-{mesh_par}-{step:04d}vtu" % (mesh_par, step),
                     [("u", u)]
                 )