diff --git a/data_structures/arrays/sudoku_solver.py b/data_structures/arrays/sudoku_solver.py
index 5c1cff06f..a8157a520 100644
--- a/data_structures/arrays/sudoku_solver.py
+++ b/data_structures/arrays/sudoku_solver.py
@@ -150,7 +150,7 @@ def solve_all(grids, name="", showif=0.0):
             display(grid_values(grid))
             if values:
                 display(values)
-            print("(%.5f seconds)\n" % t)
+            print(f"({t:.5f} seconds)\n")
         return (t, solved(values))
 
     times, results = zip(*[time_solve(grid) for grid in grids])
@@ -217,4 +217,4 @@ if __name__ == "__main__":
         start = time.monotonic()
         solve(puzzle)
         t = time.monotonic() - start
-        print("Solved: %.5f sec" % t)
+        print(f"Solved: {t:.5f} sec")
diff --git a/neural_network/input_data.py b/neural_network/input_data.py
index d189e3f9e..f90287fe3 100644
--- a/neural_network/input_data.py
+++ b/neural_network/input_data.py
@@ -156,7 +156,8 @@ class _DataSet:
         self._rng = np.random.default_rng(seed1 if seed is None else seed2)
         dtype = dtypes.as_dtype(dtype).base_dtype
         if dtype not in (dtypes.uint8, dtypes.float32):
-            raise TypeError("Invalid image dtype %r, expected uint8 or float32" % dtype)
+            msg = f"Invalid image dtype {dtype!r}, expected uint8 or float32"
+            raise TypeError(msg)
         if fake_data:
             self._num_examples = 10000
             self.one_hot = one_hot