Rationalise handling of set_auto_chartostring in threadsafe/encoded netcdf wrappers.

Author: pp-mo

lib/iris/fileformats/cf.py

@@ -1344,12 +1344,9 @@ def __init__(self, file_source, warn=False, monotonic=False):
             self._with_ugrid = False
 
         # Read the variables in the dataset only once to reduce runtime.
-        # Turn off *any* automatic decoding in the underlying netCDF4 dataset
         ds = self._dataset
-        if isinstance(ds, _thread_safe_nc.DatasetWrapper):
-            ds._contained_instance.set_auto_chartostring(False)
-        else:
-            ds.set_auto_chartostring(False)
+        # Turn off *any* automatic decoding in the underlying netCDF4 dataset.
+        ds.set_auto_chartostring(False)
         variables = self._dataset.variables
         self._translate(variables)
         self._build_cf_groups(variables)

lib/iris/fileformats/netcdf/_bytecoding_datasets.py

@@ -327,7 +327,15 @@ def _identify_encoding(encoding, var_name: str, writing: bool = False) -> str:
     return result
 
 
-class EncodedVariable(VariableWrapper):
+class Mixin_Block_AutoChartostring:
+    def set_auto_chartostring(self, onoff: bool):
+        # Silently allow a call to "turn it off", but not on.
+        if onoff:
+            msg = "auto_chartostring is not supported by Iris 'EncodedVariable' type."
+            raise TypeError(msg)
+
+
+class EncodedVariable(VariableWrapper, Mixin_Block_AutoChartostring):
     """A variable wrapper that translates variable data according to byte encodings."""
 
     def __init__(self, *args, **kwargs):
@@ -380,26 +388,18 @@ def __setitem__(self, keys, data):
         data = encoding_spec.encode_strings_as_bytearray(data)
         super().__setitem__(keys, data)
 
-    def set_auto_chartostring(self, onoff: bool):
-        msg = "auto_chartostring is not supported by Iris 'EncodedVariable' type."
-        raise TypeError(msg)
-
 
-class EncodedGroup(GroupWrapper):
+class EncodedGroup(GroupWrapper, Mixin_Block_AutoChartostring):
     """A specialised GroupWrapper whose variables are EncodedVariables."""
 
     VAR_WRAPPER_CLS = EncodedVariable
     GRP_WRAPPER_CLS: Any | None = None
 
-    def set_auto_chartostring(self, onoff: bool):
-        msg = "auto_chartostring is not supported by Iris 'EncodedGroup' type."
-        raise TypeError(msg)
-
 
 EncodedGroup.GRP_WRAPPER_CLS = EncodedGroup
 
 
-class EncodedDataset(DatasetWrapper):
+class EncodedDataset(DatasetWrapper, Mixin_Block_AutoChartostring):
     """A specialised DatasetWrapper.
 
     Its groups are EncodedGroups and variables are EncodedVariables.
@@ -408,10 +408,6 @@ class EncodedDataset(DatasetWrapper):
     VAR_WRAPPER_CLS = EncodedVariable
     GRP_WRAPPER_CLS = EncodedGroup
 
-    def set_auto_chartostring(self, onoff: bool):
-        msg = "auto_chartostring is not supported by Iris 'EncodedGroup' type."
-        raise TypeError(msg)
-
 
 class EncodedNetCDFDataProxy(NetCDFDataProxy):
     __slots__ = NetCDFDataProxy.__slots__ + ("encoding_details",)

lib/iris/fileformats/netcdf/_thread_safe_nc.py

@@ -149,6 +149,10 @@ def get_dims(self, *args, **kwargs) -> typing.Tuple[DimensionWrapper]:
             dimensions_ = list(self._contained_instance.get_dims(*args, **kwargs))
         return tuple([DimensionWrapper.from_existing(d) for d in dimensions_])
 
+    def set_auto_chartostring(self, onoff: bool):
+        with _GLOBAL_NETCDF4_LOCK:
+            self._contained_instance.set_auto_chartostring(onoff)
+
 
 class GroupWrapper(_ThreadSafeWrapper):
     """Accessor for a netCDF4.Group, always acquiring _GLOBAL_NETCDF4_LOCK.
@@ -287,6 +291,10 @@ def createGroup(self, *args, **kwargs):
             new_group = self._contained_instance.createGroup(*args, **kwargs)
         return self.GRP_WRAPPER_CLS.from_existing(new_group)
 
+    def set_auto_chartostring(self, onoff: bool):
+        with _GLOBAL_NETCDF4_LOCK:
+            self._contained_instance.set_auto_chartostring(onoff)
+
 
 GroupWrapper.GRP_WRAPPER_CLS = GroupWrapper
 
@@ -314,6 +322,10 @@ def fromcdl(cls, *args, **kwargs):
             instance = cls.CONTAINED_CLASS.fromcdl(*args, **kwargs)
         return cls.from_existing(instance)
 
+    def set_auto_chartostring(self, onoff: bool):
+        with _GLOBAL_NETCDF4_LOCK:
+            self._contained_instance.set_auto_chartostring(onoff)
+
 
 class NetCDFDataProxy:
     """A reference to the data payload of a single NetCDF file variable."""