Backport PR #5054: BUG: fix error message when trying to load a Parth…

…enon dataset without h5py installed

yt/frontends/parthenon/data_structures.py

@@ -129,6 +129,7 @@ def _populate_grid_objects(self):
 
 
 class ParthenonDataset(Dataset):
+    _load_requirements = ["h5py"]
     _field_info_class = ParthenonFieldInfo
     _dataset_type = "parthenon"
     _index_class = ParthenonHierarchy
@@ -312,6 +313,8 @@ def _parse_parameter_file(self):
 
     @classmethod
     def _is_valid(cls, filename: str, *args, **kwargs) -> bool:
+        if cls._missing_load_requirements():
+            return False
         return filename.endswith((".phdf", ".rhdf"))
 
     @property