refactor: use pathlib.Path with_suffix method to save libE output to pickle and np + Correctly parse Path to str when saving history every kth sim step

Author: soto-raul

libensemble/manager.py

@@ -339,7 +339,7 @@ def _save_every_k(self, fname: str, count: int, k: int, complete: bool) -> None:
     def _save_every_k_sims(self, complete: bool) -> None:
         """Saves history every kth sim step"""
         self._save_every_k(
-            Path(self.libE_specs["workflow_dir_path"]) / "{}_{}after_sim_{}.npy",
+            str(Path(self.libE_specs["workflow_dir_path"]) / "{}_{}after_sim_{}.npy"),
             self.hist.sim_ended_count,
             self.libE_specs["save_every_k_sims"],
             complete,

libensemble/tools/tools.py

@@ -161,10 +161,10 @@ def save_libE_output(
     logger.info(f"{status_mess}\nSaving results to file: {h_filename}")
     np.save(h_filename, H)
 
-    with open(p_filename + ".pickle", "wb") as f:
+    with open(p_filename.with_suffix(".pickle"), "wb") as f:
         pickle.dump(persis_info, f)
 
-    return h_filename + ".npy"
+    return str(h_filename.with_suffix(".npy"))
 
 
 # ===================== per-process numpy random-streams =======================