merge maybe_decode_bytes function into _read_attributes, add attribut…

…e and variable name to warning

xarray/backends/h5netcdf_.py

@@ -59,26 +59,23 @@ def _getitem(self, key):
             return array[key]
 
 
-def maybe_decode_bytes(txt):
-    if isinstance(txt, bytes):
-        try:
-            return txt.decode("utf-8")
-        except UnicodeDecodeError:
-            emit_user_level_warning(
-                "'utf-8' codec can't decode bytes, " "returning bytes undecoded.",
-                UnicodeWarning,
-            )
-    return txt
-
-
 def _read_attributes(h5netcdf_var):
     # GH451
     # to ensure conventions decoding works properly on Python 3, decode all
     # bytes attributes to strings
     attrs = {}
     for k, v in h5netcdf_var.attrs.items():
         if k not in ["_FillValue", "missing_value"]:
-            v = maybe_decode_bytes(v)
+            if isinstance(v, bytes):
+                try:
+                    v = v.decode("utf-8")
+                except UnicodeDecodeError:
+                    emit_user_level_warning(
+                        f"'utf-8' codec can't decode bytes for attribute "
+                        f"{k!r} of h5netcdf object {h5netcdf_var.name!r}, "
+                        f"returning bytes undecoded.",
+                        UnicodeWarning,
+                    )
         attrs[k] = v
     return attrs
 

xarray/tests/test_backends.py

@@ -3565,9 +3565,10 @@ def test_decode_utf8_warning(self) -> None:
         with create_tmp_file() as tmp_file:
             with nc4.Dataset(tmp_file, "w") as f:
                 f.title = title
-            with pytest.warns(UnicodeWarning, match="returning bytes undecoded"):
+            with pytest.warns(UnicodeWarning, match="returning bytes undecoded") as w:
                 ds = xr.load_dataset(tmp_file, engine="h5netcdf")
                 assert ds.title == title
+                assert "attribute 'title' of h5netcdf object '/'" in str(w[0].message)
 
 
 @requires_h5netcdf