Chardata plus encodedarrays

lib/iris/fileformats/_nc_load_rules/helpers.py

@@ -708,13 +708,13 @@ def build_and_add_global_attributes(engine: Engine):
             ),
         )
         if problem is not None:
-            stack_notes = problem.stack_trace.__notes__
+            stack_notes = problem.stack_trace.__notes__  # type: ignore[attr-defined]
             if stack_notes is None:
                 stack_notes = []
             stack_notes.append(
                 f"Skipping disallowed global attribute '{attr_name}' (see above error)"
             )
-            problem.stack_trace.__notes__ = stack_notes
+            problem.stack_trace.__notes__ = stack_notes  # type: ignore[attr-defined]
 
 
 ################################################################################
@@ -1536,14 +1536,14 @@ def build_and_add_dimension_coordinate(
     )
     if problem is not None:
         coord_var_name = str(cf_coord_var.cf_name)
-        stack_notes = problem.stack_trace.__notes__
+        stack_notes = problem.stack_trace.__notes__  # type: ignore[attr-defined]
         if stack_notes is None:
             stack_notes = []
         stack_notes.append(
             f"Failed to create {coord_var_name} dimension coordinate:\n"
             f"Gracefully creating {coord_var_name!r} auxiliary coordinate instead."
         )
-        problem.stack_trace.__notes__ = stack_notes
+        problem.stack_trace.__notes__ = stack_notes  # type: ignore[attr-defined]
         problem.handled = True
 
         _ = _add_or_capture(
@@ -1643,9 +1643,13 @@ def _add_auxiliary_coordinate(
 
     # Determine the name of the dimension/s shared between the CF-netCDF data variable
     # and the coordinate being built.
-    common_dims = [
-        dim for dim in cf_coord_var.dimensions if dim in engine.cf_var.dimensions
-    ]
+    coord_dims = cf_coord_var.dimensions
+    if cf._is_str_dtype(cf_coord_var):
+        coord_dims = coord_dims[:-1]
+    datavar_dims = engine.cf_var.dimensions
+    if cf._is_str_dtype(engine.cf_var):
+        datavar_dims = datavar_dims[:-1]
+    common_dims = [dim for dim in coord_dims if dim in datavar_dims]
     data_dims = None
     if common_dims:
         # Calculate the offset of each common dimension.

lib/iris/fileformats/cf.py

@@ -26,7 +26,7 @@
 
 import iris.exceptions
 import iris.fileformats._nc_load_rules.helpers as hh
-from iris.fileformats.netcdf import _thread_safe_nc
+from iris.fileformats.netcdf import _bytecoding_datasets
 from iris.mesh.components import Connectivity
 import iris.util
 import iris.warnings
@@ -790,19 +790,31 @@ def cf_label_data(self, cf_data_var):
 
         # Determine the name of the label string (or length) dimension by
         # finding the dimension name that doesn't exist within the data dimensions.
-        str_dim_name = list(set(self.dimensions) - set(cf_data_var.dimensions))
+        str_dim_names = list(set(self.dimensions) - set(cf_data_var.dimensions))
+        n_nondata_dims = len(str_dim_names)
+
+        if n_nondata_dims == 0:
+            # *All* dims are shared with the data-variable.
+            # This is only ok if the data-var is *also* a string type.
+            dim_ok = _is_str_dtype(cf_data_var)
+            # In this case, we must just *assume* that the last dimension is "the"
+            #  string dimension
+            str_dim_name = self.dimensions[-1]
+        else:
+            # If there is exactly one non-data dim, that is the one we want
+            dim_ok = len(str_dim_names) == 1
+            (str_dim_name,) = str_dim_names
 
-        if len(str_dim_name) != 1:
+        if not dim_ok:
             raise ValueError(
                 "Invalid string dimensions for CF-netCDF label variable %r"
                 % self.cf_name
             )
 
-        str_dim_name = str_dim_name[0]
         label_data = self[:]
 
         if ma.isMaskedArray(label_data):
-            label_data = label_data.filled()
+            label_data = label_data.filled(b"\0")
 
         # Determine whether we have a string-valued scalar label
         # i.e. a character variable that only has one dimension (the length of the string).
@@ -1361,7 +1373,9 @@ def __init__(self, file_source, warn=False, monotonic=False):
         if isinstance(file_source, str):
             # Create from filepath : open it + own it (=close when we die).
             self._filename = os.path.expanduser(file_source)
-            self._dataset = _thread_safe_nc.DatasetWrapper(self._filename, mode="r")
+            self._dataset = _bytecoding_datasets.EncodedDataset(
+                self._filename, mode="r"
+            )
             self._own_file = True
         else:
             # We have been passed an open dataset.