From 2b4fbebe3587f11e61405f2605fbeb86f50a1548 Mon Sep 17 00:00:00 2001
From: David Hassell <david.hassell@ncas.ac.uk>
Date: Wed, 24 Sep 2025 16:02:26 +0100
Subject: [PATCH 01/10] dev

---
 Changelog.rst                | 11 +++++++++++
 README.md                    |  3 ++-
 docs/source/installation.rst |  6 ++++++
 docs/source/introduction.rst |  7 ++++---
 docs/source/tutorial.rst     |  9 ++++++---
 setup.py                     |  7 +++++--
 6 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/Changelog.rst b/Changelog.rst
index d6ab07043d..502f931519 100644
--- a/Changelog.rst
+++ b/Changelog.rst
@@ -1,3 +1,14 @@
+Version NEXTVERSION
+--------------
+
+* Write Zarr v3 datasets with `cf.write`, and allow the reading of
+  grouped Zarr v2 and v3 datasets with `cf.read`
+  (https://github.com/NCAS-CMS/cf-python/issues/895)
+* Read Zarr v2 and v3 datasets that contain a group hierarchy with
+  `cf.read` (https://github.com/NCAS-CMS/cf-python/issues/894)
+
+----
+
 Version 3.18.1
 --------------
 
diff --git a/README.md b/README.md
index ce752fd0af..45c70a4f17 100644
--- a/README.md
+++ b/README.md
@@ -87,7 +87,8 @@ of its array manipulation and can:
 * read field constructs from netCDF, CDL, Zarr, PP and UM datasets with a
   choice of netCDF backends,and in local, http, and s3 locations,
 * create new field constructs in memory,
-* write and append field and domain constructs to netCDF datasets on disk,
+* write and append field and domain constructs to netCDF and Zarr v3
+  datasets on disk,
 * read, create, and manipulate UGRID mesh topologies,
 * read, write, and create coordinates defined by geometry cells,
 * read netCDF and CDL datasets containing hierarchical groups,
diff --git a/docs/source/installation.rst b/docs/source/installation.rst
index 40cec52247..29c7820947 100644
--- a/docs/source/installation.rst
+++ b/docs/source/installation.rst
@@ -265,6 +265,12 @@ Some further dependencies that enable further functionality are
 optional. This to facilitate cf-python being installed in restricted
 environments for which these features are not required.
 
+.. rubric:: Zarr
+
+* `zarr <https://pypi.org/project/zarr>`_, version 3.1.2 or newer.
+
+  For reading and writing Zarr datasets.
+    
 .. rubric:: Regridding
 
 * `esmpy <https://earthsystemmodeling.org/esmpy/>`_, previously
diff --git a/docs/source/introduction.rst b/docs/source/introduction.rst
index ca7789acb7..ee27ac47fb 100644
--- a/docs/source/introduction.rst
+++ b/docs/source/introduction.rst
@@ -67,8 +67,8 @@ may nonetheless be modified in memory.
 The `cf` package can:
 
 * read :term:`field constructs <field construct>` and :term:`domain
-  constructs <domain construct>` from netCDF, CDL, PP and UM datasets
-  with a choice of netCDF backends,
+  constructs <domain construct>` from netCDF, CDL, Zarr, PP and UM
+  datasets with a choice of netCDF backends,
 
 * read files from OPeNDAP servers and S3 object stores,
 
@@ -76,7 +76,8 @@ The `cf` package can:
 
 * create new field constructs in memory,
 
-* write and append field constructs to netCDF datasets on disk,
+* write and append field and domain constructs to netCDF and Zarr
+  datasets on disk,
 
 * read, write, and manipulate UGRID mesh topologies,
 
diff --git a/docs/source/tutorial.rst b/docs/source/tutorial.rst
index 4b6806b619..9d501c91de 100644
--- a/docs/source/tutorial.rst
+++ b/docs/source/tutorial.rst
@@ -5275,8 +5275,11 @@ Method                                         Classes
 **Writing to a netCDF dataset**
 -------------------------------
 
+**Writing to disk**
+-------------------
+
 The `cf.write` function writes a field construct, or a sequence of
-field constructs, to a new netCDF file on disk:
+field constructs, to a netCDF or Zarr dataset on disk:
 
 .. code-block:: python
    :caption: *Write a field construct to a netCDF dataset on disk.*
@@ -5345,8 +5348,8 @@ By default the output file will be for CF-|version|.
    
 The `cf.write` function has optional parameters to
 
-* set the output netCDF format (all netCDF3 and netCDF4 formats are
-  possible);
+* set the output netCDF format (all netCDF3 and netCDF4 formats, as
+  well as Zarr v3 are possible);
 
 * append to the netCDF file rather than over-writing it by default;
 
diff --git a/setup.py b/setup.py
index f82bd9182d..6241d9ad3f 100755
--- a/setup.py
+++ b/setup.py
@@ -177,13 +177,13 @@ def compile():
 
 The ``cf`` package can:
 
-* read field constructs from netCDF, CDL, Zarr, PP and UM datasets,
+* read field and domain constructs from netCDF, CDL, Zarr, PP and UM datasets,
 
 * be fully flexible with respect to dataset storage chunking,
 
 * create new field constructs in memory,
 
-* write and append field constructs to netCDF datasets on disk,
+* write and append field constructs and domain to netCDF and Zarr v3 datasets on disk,
 
 * read, write, and create coordinates defined by geometry cells,
 
@@ -262,6 +262,9 @@ def compile():
         "docformatter",
         "flake8",
     ],
+    "zarr": [
+        "zarr>=3.1.2",
+    ],
 }
 
 setup(

From dbbecf8b5f0346d6d777ed2b4dcce716fdb4bb25 Mon Sep 17 00:00:00 2001
From: David Hassell <david.hassell@ncas.ac.uk>
Date: Mon, 20 Oct 2025 17:52:14 +0100
Subject: [PATCH 02/10] dev

---
 Changelog.rst                |   1 +
 cf/test/test_zarr.py         | 333 +++++++++++++++++++++++++++++++++++
 docs/source/installation.rst |   2 +-
 3 files changed, 335 insertions(+), 1 deletion(-)
 create mode 100644 cf/test/test_zarr.py

diff --git a/Changelog.rst b/Changelog.rst
index 6bee2feca2..5546cf55db 100644
--- a/Changelog.rst
+++ b/Changelog.rst
@@ -6,6 +6,7 @@ Version NEXTVERSION
   (https://github.com/NCAS-CMS/cf-python/issues/895)
 * Read Zarr v2 and v3 datasets that contain a group hierarchy with
   `cf.read` (https://github.com/NCAS-CMS/cf-python/issues/894)
+* New optional dependency: ``zarr>=3.1.2``
 
 Version 3.18.2
 --------------
diff --git a/cf/test/test_zarr.py b/cf/test/test_zarr.py
new file mode 100644
index 0000000000..2310a83953
--- /dev/null
+++ b/cf/test/test_zarr.py
@@ -0,0 +1,333 @@
+import atexit
+import datetime
+import faulthandler
+import os
+import shutil
+import tempfile
+import unittest
+
+faulthandler.enable()  # to debug seg faults and timeouts
+
+import zarr
+
+import cf
+
+warnings = False
+
+# Set up temporary directories
+tmpdirs = [
+    tempfile.mkdtemp("_test_zarr.zarr", dir=os.getcwd()) for i in range(2)
+]
+[tmpdir1, tmpdir2] = tmpdirs
+
+# Set up temporary files
+tmpfiles = [
+    tempfile.mkstemp("_test_zarr.nc", dir=os.getcwd())[1] for i in range(2)
+]
+[tmpfile1, tmpfile2] = tmpfiles
+
+
+def _remove_tmpdirs():
+    """Remove temporary files created during tests."""
+    for f in tmpfiles:
+        try:
+            os.remove(f)
+        except OSError:
+            pass
+
+    for d in tmpdirs:
+        try:
+            shutil.rmtree(d)
+            os.rmdir(d)
+        except OSError:
+            pass
+
+
+atexit.register(_remove_tmpdirs)
+
+
+class read_writeTest(unittest.TestCase):
+    """Test the reading and writing of field constructs from/to disk."""
+
+    f0 = cf.example_field(0)
+
+    def setUp(self):
+        """Preparations called immediately before each test method."""
+        # Disable log messages to silence expected warnings
+        cf.LOG_LEVEL("DISABLE")
+        # Note: to enable all messages for given methods, lines or
+        # calls (those without a 'verbose' option to do the same)
+        # e.g. to debug them, wrap them (for methods, start-to-end
+        # internally) as follows: cf.LOG_LEVEL('DEBUG')
+        #
+        # < ... test code ... >
+        # cf.log_level('DISABLE')
+
+    def test_zarr_read_write_1(self):
+        """Test Zarr read/write on example fields."""
+        for i, f in enumerate(cf.example_fields()):
+            if i in (8, 9, 10):
+                # Can't write UGRID yet
+                continue
+
+            cf.write(f, tmpdir1, fmt="ZARR3")
+            z = cf.read(tmpdir1)
+            self.assertEqual(len(z), 1)
+            z = z[0]
+            self.assertTrue(z.equals(f))
+
+            # Check that the Zarr and netCDF4 encodings are equivalent
+            cf.write(f, tmpfile1, fmt="NETCDF4")
+            n = cf.read(tmpfile1)[0]
+            self.assertTrue(z.equals(n))
+
+    def test_zarr_read_write_2(self):
+        """Test Zarr read/write on various netCDF files."""
+        for filename in (
+            "DSG_timeSeries_contiguous.nc",
+            "DSG_timeSeries_indexed.nc",
+            "DSG_timeSeriesProfile_indexed_contiguous.nc",
+            "gathered.nc",
+            "geometry_1.nc",
+            "geometry_2.nc",
+            "geometry_3.nc",
+            "geometry_4.nc",
+            "string_char.nc",
+        ):
+            n = cf.read(filename)
+            cf.write(n, tmpdir1, fmt="ZARR3")
+            z = cf.read(tmpdir1)
+            self.assertEqual(len(z), len(n))
+            for a, b in zip(z, n):
+                self.assertTrue(a.equals(b))
+
+    def test_zarr_read_write_chunks_shards(self):
+        """Test Zarr read/write with chunks and shards."""
+        f = self.f0.copy()
+        f.data.nc_set_dataset_chunksizes([2, 3])
+
+        cf.write(f, tmpdir1, fmt="ZARR3")
+        z = cf.read(tmpdir1)[0]
+        self.assertTrue(z.equals(f))
+
+        z = zarr.open(tmpdir1)
+        self.assertEqual(z["q"].chunks, (2, 3))
+        self.assertIsNone(z["q"].shards)
+
+        # Make shards comprising 4 chunks
+        cf.write(f, tmpdir1, fmt="ZARR3", dataset_shards=4)
+        z = cf.read(tmpdir1, store_dataset_shards=False)[0]
+        self.assertTrue(z.equals(f))
+        self.assertIsNone(z.data.nc_dataset_shards())
+
+        z = zarr.open(tmpdir1)
+        self.assertEqual(z["q"].chunks, (2, 3))
+        self.assertEqual(z["q"].shards, (4, 6))
+
+        for shards in (4, [2, 2]):
+            f.data.nc_set_dataset_shards(shards)
+            cf.write(f, tmpdir1, fmt="ZARR3")
+            z = cf.read(tmpdir1)[0]
+            self.assertTrue(z.equals(f))
+            self.assertEqual(z.data.nc_dataset_shards(), (2, 2))
+
+            z = zarr.open(tmpdir1)
+            self.assertEqual(z["q"].chunks, (2, 3))
+            self.assertEqual(z["q"].shards, (4, 6))
+
+    def test_zarr_read_write_CFA(self):
+        """Test CF aggreagtion in Zarr."""
+        f = self.f0
+
+        cf.write(f, tmpdir1, fmt="ZARR3")
+        cf.write(f, tmpfile1, fmt="NETCDF4")
+
+        z = cf.read(tmpdir1, cfa_write="field")[0]
+        n = cf.read(tmpfile1, cfa_write="field")[0]
+
+        self.assertTrue(z.equals(f))
+        self.assertTrue(z.equals(n))
+
+        cf.write(z, tmpdir2, fmt="ZARR3", cfa="field")
+        cf.write(n, tmpfile2, fmt="NETCDF4", cfa="field")
+
+        z = cf.read(tmpdir2)[0]
+        n = cf.read(tmpfile2)[0]
+
+        self.assertTrue(z.equals(f))
+        self.assertTrue(z.equals(n))
+
+    def test_zarr_groups_1(self):
+        """Test for the general handling of Zarr hierarchical groups."""
+        f = cf.example_field(1)
+
+        # Add a second grid mapping
+        datum = cf.Datum(parameters={"earth_radius": 7000000})
+        conversion = cf.CoordinateConversion(
+            parameters={"grid_mapping_name": "latitude_longitude"}
+        )
+
+        grid = cf.CoordinateReference(
+            coordinate_conversion=conversion,
+            datum=datum,
+            coordinates=["auxiliarycoordinate0", "auxiliarycoordinate1"],
+        )
+
+        f.set_construct(grid)
+
+        grid0 = f.construct("grid_mapping_name:rotated_latitude_longitude")
+        grid0.del_coordinate("auxiliarycoordinate0")
+        grid0.del_coordinate("auxiliarycoordinate1")
+
+        grouped_dir = tmpdir1
+        grouped_file = tmpfile1
+
+        # Set some groups
+        f.nc_set_variable_groups(["forecast", "model"])
+        f.construct("grid_latitude").bounds.nc_set_variable_groups(
+            ["forecast"]
+        )
+        for name in (
+            "longitude",  # Auxiliary coordinate
+            "latitude",  # Auxiliary coordinate
+            "long_name=Grid latitude name",  # Auxiliary coordinate
+            "measure:area",  # Cell measure
+            "surface_altitude",  # Domain ancillary
+            "air_temperature standard_error",  # Field ancillary
+            "grid_mapping_name:rotated_latitude_longitude",
+            "time",  # Dimension coordinate
+            "grid_latitude",  # Dimension coordinate
+        ):
+            f.construct(name).nc_set_variable_groups(["forecast"])
+
+        # Check the groups
+        cf.write(f, grouped_file, fmt="NETCDF4")
+        cf.write(f, grouped_dir, fmt="ZARR3")
+
+        n = cf.read(grouped_file)[0]
+        z = cf.read(grouped_dir)[0]
+        self.assertTrue(z.equals(n))
+        self.assertTrue(z.equals(f))
+
+        # Directly check the groups in the Zarr dataset
+        x = zarr.open(grouped_dir)
+        self.assertEqual(list(x.group_keys()), ["forecast"])
+        self.assertEqual(list(x["forecast"].group_keys()), ["model"])
+
+        cf.write(z, tmpdir2, fmt="ZARR3")
+        z1 = cf.read(tmpdir2)[0]
+        self.assertTrue(z1.equals(f))
+
+    def test_zarr_groups_dimension(self):
+        """Test Zarr groups dimensions."""
+        f = self.f0.copy()
+
+        grouped_dir = tmpdir1
+        grouped_file = tmpfile1
+
+        # Set some groups
+        f.nc_set_variable_groups(["forecast", "model"])
+        for construct in f.constructs.filter_by_data().values():
+            construct.nc_set_variable_groups(["forecast"])
+
+        for construct in f.coordinates().values():
+            try:
+                construct.bounds.nc_set_variable_groups(["forecast"])
+            except ValueError:
+                pass
+
+        domain_axis = f.domain_axis("latitude")
+        domain_axis.nc_set_dimension_groups(["forecast"])
+
+        # Check the groups
+        cf.write(f, grouped_file, fmt="NETCDF4")
+        cf.write(f, grouped_dir, fmt="ZARR3")
+
+        n = cf.read(grouped_file)[0]
+        z = cf.read(grouped_dir)[0]
+        self.assertTrue(z.equals(n))
+        self.assertTrue(z.equals(f))
+
+        # Check that grouped netCDF datasets can only be read with
+        # 'closest_ancestor'
+        cf.read(grouped_file, group_dimension_search="closest_ancestor")
+        for gsn in ("furthest_ancestor", "local", "BAD VALUE"):
+            with self.assertRaises(ValueError):
+                cf.read(grouped_file, group_dimension_search=gsn)
+
+    def test_zarr_groups_DSG(self):
+        """Test Zarr groups containing DSGs."""
+        f = cf.example_field(4)
+
+        grouped_dir = tmpdir1
+        grouped_file = tmpfile1
+
+        f.compress("indexed_contiguous", inplace=True)
+        f.data.get_count().nc_set_variable("count")
+        f.data.get_index().nc_set_variable("index")
+
+        # Set some groups. (Write the read the field first to create
+        # the compressions variables on disk.)
+        cf.write(f, tmpfile2)
+        f = cf.read(tmpfile2)[0]
+
+        # Set some groups
+        f.nc_set_variable_groups(["forecast", "model"])
+        f.data.get_count().nc_set_variable_groups(["forecast"])
+        f.data.get_index().nc_set_variable_groups(["forecast"])
+        f.construct("altitude").nc_set_variable_groups(["forecast"])
+        f.data.get_count().nc_set_sample_dimension_groups(["forecast"])
+
+        cf.write(f, grouped_file, fmt="NETCDF4")
+        cf.write(f, grouped_dir, fmt="ZARR3")
+
+        n = cf.read(grouped_file)
+        z = cf.read(grouped_dir)
+
+        n = n[0]
+        z = z[0]
+        self.assertTrue(z.equals(n))
+        self.assertTrue(z.equals(f))
+
+    def test_zarr_groups_geometry(self):
+        """Test Zarr groups containing cell geometries."""
+        f = cf.example_field(6)
+
+        grouped_dir = tmpdir1
+        grouped_file = tmpfile1
+
+        cf.write(f, tmpfile2)
+        f = cf.read(tmpfile2)[0]
+
+        # Set some groups
+        f.nc_set_variable_groups(["forecast", "model"])
+        f.nc_set_geometry_variable_groups(["forecast"])
+        f.coordinate("longitude").bounds.nc_set_variable_groups(["forecast"])
+        f.nc_set_component_variable_groups("node_count", ["forecast"])
+        f.nc_set_component_variable_groups("part_node_count", ["forecast"])
+        f.nc_set_component_variable("interior_ring", "interior_ring")
+        f.nc_set_component_variable_groups("interior_ring", ["forecast"])
+
+        # Check the groups
+        cf.write(f, grouped_file, fmt="NETCDF4")
+        cf.write(f, grouped_dir, fmt="ZARR3")
+
+        n = cf.read(grouped_file)[0]
+        z = cf.read(grouped_dir)[0]
+        self.assertTrue(z.equals(n))
+        self.assertTrue(z.equals(f))
+
+    def test_zarr_read_v2(self):
+        """Test reading Zarr v2."""
+        f2 = cf.read("example_field_0.zarr2")
+        f3 = cf.read("example_field_0.zarr3")
+        self.assertEqual(len(f2), len(f3))
+        self.assertEqual(len(f2), 1)
+        self.assertTrue(f2[0].equals(f3[0]))
+
+
+if __name__ == "__main__":
+    print("Run date:", datetime.datetime.now())
+    cf.environment()
+    print("")
+    unittest.main(verbosity=2)
diff --git a/docs/source/installation.rst b/docs/source/installation.rst
index 2d3bd43d4d..6309432127 100644
--- a/docs/source/installation.rst
+++ b/docs/source/installation.rst
@@ -270,7 +270,7 @@ environments for which these features are not required.
 * `zarr <https://pypi.org/project/zarr>`_, version 3.1.2 or newer.
 
   For reading and writing Zarr datasets.
-    
+
 .. rubric:: Regridding
 
 * `esmpy <https://earthsystemmodeling.org/esmpy/>`_, previously

From 276f5645b3ddd106544d1c5a2ee8ec51344af2eb Mon Sep 17 00:00:00 2001
From: David Hassell <david.hassell@ncas.ac.uk>
Date: Mon, 27 Oct 2025 14:01:14 +0000
Subject: [PATCH 03/10] dev

---
 cf/read_write/um/umread.py            | 16 ++++++++--------
 docs/source/conf.py                   |  3 +--
 docs/source/recipes/plot_08_recipe.py |  3 +--
 docs/source/recipes/plot_12_recipe.py |  2 +-
 docs/source/recipes/plot_13_recipe.py |  4 +---
 docs/source/recipes/plot_17_recipe.py |  2 +-
 docs/source/recipes/plot_18_recipe.py |  4 ++--
 docs/source/recipes/plot_19_recipe.py |  8 ++++++--
 docs/source/recipes/plot_22_recipe.py |  5 +++--
 docs/source/recipes/plot_23_recipe.py |  8 ++++----
 10 files changed, 28 insertions(+), 27 deletions(-)

diff --git a/cf/read_write/um/umread.py b/cf/read_write/um/umread.py
index 3289ea88b4..1451578440 100644
--- a/cf/read_write/um/umread.py
+++ b/cf/read_write/um/umread.py
@@ -3566,7 +3566,7 @@ def read(
                 # Return now if there are valid file types
                 return []
 
-        f = self.file_open(filename, parse=True)
+        f = self.dataset_open(filename, parse=True)
 
         info = is_log_level_info(logger)
 
@@ -3589,7 +3589,7 @@ def read(
             for var in f.vars
         ]
 
-        self.file_close()
+        self.dataset_close()
 
         return [field for x in um for field in x.fields if field]
 
@@ -3623,7 +3623,7 @@ def _open_um_file(
                 The open PP or FF file object.
 
         """
-        self.file_close()
+        self.dataset_close()
         try:
             f = File(
                 filename,
@@ -3669,15 +3669,15 @@ def is_um_file(self, filename):
         try:
             # Note: No need to completely parse the file to ascertain
             #       if it's PP or FF.
-            self.file_open(filename, parse=False)
+            self.dataset_open(filename, parse=False)
         except Exception:
-            self.file_close()
+            self.dataset_close()
             return False
         else:
-            self.file_close()
+            self.dataset_close()
             return True
 
-    def file_close(self):
+    def dataset_close(self):
         """Close the file that has been read.
 
         :Returns:
@@ -3691,7 +3691,7 @@ def file_close(self):
 
         self._um_file = None
 
-    def file_open(self, filename, parse=True):
+    def dataset_open(self, filename, parse=True):
         """Open the file for reading.
 
         :Paramters:
diff --git a/docs/source/conf.py b/docs/source/conf.py
index 239aa988fa..4f45911a65 100755
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -389,7 +389,7 @@ def _get_date():
     "run_stale_examples": False,
     # Below setting can be buggy: see:
     # https://github.com/sphinx-gallery/sphinx-gallery/issues/967
-    #"reference_url": {"cf": None},
+    # "reference_url": {"cf": None},
     "backreferences_dir": "gen_modules/backreferences",
     "doc_module": ("cf",),
     "inspect_global_variables": True,
@@ -476,7 +476,6 @@ def _get_date():
 import cf
 
 
-
 def linkcode_resolve(domain, info):
     # =================================================================
     # Must delete all .doctrees directories in build for changes to be
diff --git a/docs/source/recipes/plot_08_recipe.py b/docs/source/recipes/plot_08_recipe.py
index 63427f62a7..6045f51448 100644
--- a/docs/source/recipes/plot_08_recipe.py
+++ b/docs/source/recipes/plot_08_recipe.py
@@ -9,11 +9,10 @@
 # 1. Import cf-python, cf-plot, numpy and scipy.stats:
 
 import cfplot as cfp
-import cf
-
 import numpy as np
 import scipy.stats as stats
 
+import cf
 
 # %%
 # 2. Three functions are defined:
diff --git a/docs/source/recipes/plot_12_recipe.py b/docs/source/recipes/plot_12_recipe.py
index b09db0b29f..5304194b19 100644
--- a/docs/source/recipes/plot_12_recipe.py
+++ b/docs/source/recipes/plot_12_recipe.py
@@ -13,8 +13,8 @@
 # %%
 # 1. Import cf-python, cf-plot and matplotlib.pyplot:
 
-import matplotlib.pyplot as plt
 import cfplot as cfp
+import matplotlib.pyplot as plt
 
 import cf
 
diff --git a/docs/source/recipes/plot_13_recipe.py b/docs/source/recipes/plot_13_recipe.py
index bf0398713e..9b658597d8 100644
--- a/docs/source/recipes/plot_13_recipe.py
+++ b/docs/source/recipes/plot_13_recipe.py
@@ -18,13 +18,11 @@
 # in next steps.
 
 import cartopy.crs as ccrs
-import matplotlib.patches as mpatches
-
 import cfplot as cfp
+import matplotlib.patches as mpatches
 
 import cf
 
-
 # %%
 # 2. Read and select the SST by index and look at its contents:
 sst = cf.read("~/recipes/ERA5_monthly_averaged_SST.nc")[0]
diff --git a/docs/source/recipes/plot_17_recipe.py b/docs/source/recipes/plot_17_recipe.py
index c94769e2ba..a66c90b518 100644
--- a/docs/source/recipes/plot_17_recipe.py
+++ b/docs/source/recipes/plot_17_recipe.py
@@ -11,8 +11,8 @@
 # %%
 # 1. Import cf-python and cf-plot:
 
-import matplotlib.pyplot as plt
 import cfplot as cfp
+import matplotlib.pyplot as plt
 
 import cf
 
diff --git a/docs/source/recipes/plot_18_recipe.py b/docs/source/recipes/plot_18_recipe.py
index f0eae36e35..3beb9d0db9 100644
--- a/docs/source/recipes/plot_18_recipe.py
+++ b/docs/source/recipes/plot_18_recipe.py
@@ -10,15 +10,15 @@
 
 """
 
+import cfplot as cfp
+
 # %%
 # 1. Import cf-python, cf-plot and other required packages:
 import matplotlib.pyplot as plt
 import scipy.stats.mstats as mstats
-import cfplot as cfp
 
 import cf
 
-
 # %%
 # 2. Read the data in and unpack the Fields from FieldLists using indexing.
 # In our example We are investigating the influence of the land height on
diff --git a/docs/source/recipes/plot_19_recipe.py b/docs/source/recipes/plot_19_recipe.py
index dcc0926fbd..ceb9db1c5c 100644
--- a/docs/source/recipes/plot_19_recipe.py
+++ b/docs/source/recipes/plot_19_recipe.py
@@ -9,10 +9,11 @@
 maxima.
 """
 
+import cfplot as cfp
+
 # %%
 # 1. Import cf-python, cf-plot and other required packages:
 import matplotlib.pyplot as plt
-import cfplot as cfp
 
 import cf
 
@@ -55,7 +56,10 @@
 # of the maxima, we loop through the season query mapping and do a
 # "T: mean" collapse setting the season as the grouping:
 cfp.gopen(
-    rows=2, columns=1, bottom=0.1, top=0.85,
+    rows=2,
+    columns=1,
+    bottom=0.1,
+    top=0.85,
 )
 cfp.gpos(1)
 cfp.gset(xmin="1980-01-01", xmax="2022-12-01", ymin=304, ymax=312)
diff --git a/docs/source/recipes/plot_22_recipe.py b/docs/source/recipes/plot_22_recipe.py
index 377313c899..fe329cda9d 100644
--- a/docs/source/recipes/plot_22_recipe.py
+++ b/docs/source/recipes/plot_22_recipe.py
@@ -11,10 +11,11 @@
 # %%
 # 1. Import cf-python, Dask.array, NumPy, and Matplotlib:
 
-import cf
 import dask.array as da
-import numpy as np
 import matplotlib.pyplot as plt
+import numpy as np
+
+import cf
 
 # %%
 # 2. Read the field constructs and load the wind speed component fields:
diff --git a/docs/source/recipes/plot_23_recipe.py b/docs/source/recipes/plot_23_recipe.py
index 2499b0d875..29537803af 100644
--- a/docs/source/recipes/plot_23_recipe.py
+++ b/docs/source/recipes/plot_23_recipe.py
@@ -18,12 +18,12 @@
 # sphinx_gallery_thumbnail_number = 2
 # sphinx_gallery_end_ignore
 
-import matplotlib.pyplot as plt
 import cfplot as cfp
-import cf
-
-import numpy as np
 import dask.array as da
+import matplotlib.pyplot as plt
+import numpy as np
+
+import cf
 
 # %%
 # 2. Read example data field constructs, and set region for our plots:

From 7a27417c6798c8b4743d26905a0e340e2b52e48a Mon Sep 17 00:00:00 2001
From: David Hassell <david.hassell@ncas.ac.uk>
Date: Thu, 13 Nov 2025 18:50:40 +0000
Subject: [PATCH 04/10] dev

---
 cf/functions.py              | 4 ++--
 docs/source/installation.rst | 2 +-
 setup.py                     | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/cf/functions.py b/cf/functions.py
index f63b037305..daf30b8560 100644
--- a/cf/functions.py
+++ b/cf/functions.py
@@ -3184,7 +3184,7 @@ def environment(display=True, paths=True):
     netCDF4: 1.7.2 /home/miniconda3/lib/python3.12/site-packages/netCDF4/__init__.py
     h5netcdf: 1.3.0 /home/miniconda3/lib/python3.12/site-packages/h5netcdf/__init__.py
     h5py: 3.12.1 /home/miniconda3/lib/python3.12/site-packages/h5py/__init__.py
-    zarr: 3.0.8 /home/miniconda3/lib/python3.12/site-packages/zarr/__init__.py
+    zarr: 3.1.3 /home/miniconda3/lib/python3.12/site-packages/zarr/__init__.py
     s3fs: 2024.12.0 /home/miniconda3/lib/python3.12/site-packages/s3fs/__init__.py
     scipy: 1.15.1 /home/miniconda3/lib/python3.12/site-packages/scipy/__init__.py
     dask: 2025.5.1 /home/miniconda3/lib/python3.12/site-packages/dask/__init__.py
@@ -3210,7 +3210,7 @@ def environment(display=True, paths=True):
     netCDF4: 1.7.2
     h5netcdf: 1.3.0
     h5py: 3.12.1
-    zarr: 3.0.8
+    zarr: 3.1.3
     s3fs: 2024.12.0
     scipy: 1.15.1
     dask: 2025.5.1
diff --git a/docs/source/installation.rst b/docs/source/installation.rst
index 6309432127..4ec36e0d67 100644
--- a/docs/source/installation.rst
+++ b/docs/source/installation.rst
@@ -267,7 +267,7 @@ environments for which these features are not required.
 
 .. rubric:: Zarr
 
-* `zarr <https://pypi.org/project/zarr>`_, version 3.1.2 or newer.
+* `zarr <https://pypi.org/project/zarr>`_, version 3.1.3 or newer.
 
   For reading and writing Zarr datasets.
 
diff --git a/setup.py b/setup.py
index 35ab6008da..a9bdd9f268 100755
--- a/setup.py
+++ b/setup.py
@@ -264,7 +264,7 @@ def compile():
         "flake8",
     ],
     "zarr": [
-        "zarr>=3.1.2",
+        "zarr>=3.1.3",
     ],
 }
 

From 4692dbb369b14bf1a5d9865bc5418efa755c23f9 Mon Sep 17 00:00:00 2001
From: David Hassell <david.hassell@ncas.ac.uk>
Date: Thu, 8 Jan 2026 16:32:02 +0000
Subject: [PATCH 05/10] reverted recipe directory

---
 docs/source/recipes/plot_08_recipe.py | 3 ++-
 docs/source/recipes/plot_12_recipe.py | 2 +-
 docs/source/recipes/plot_13_recipe.py | 4 +++-
 docs/source/recipes/plot_17_recipe.py | 2 +-
 docs/source/recipes/plot_18_recipe.py | 4 ++--
 docs/source/recipes/plot_19_recipe.py | 8 ++------
 docs/source/recipes/recipe_list.txt   | 8 +-------
 7 files changed, 12 insertions(+), 19 deletions(-)

diff --git a/docs/source/recipes/plot_08_recipe.py b/docs/source/recipes/plot_08_recipe.py
index 6045f51448..63427f62a7 100644
--- a/docs/source/recipes/plot_08_recipe.py
+++ b/docs/source/recipes/plot_08_recipe.py
@@ -9,10 +9,11 @@
 # 1. Import cf-python, cf-plot, numpy and scipy.stats:
 
 import cfplot as cfp
+import cf
+
 import numpy as np
 import scipy.stats as stats
 
-import cf
 
 # %%
 # 2. Three functions are defined:
diff --git a/docs/source/recipes/plot_12_recipe.py b/docs/source/recipes/plot_12_recipe.py
index 5304194b19..b09db0b29f 100644
--- a/docs/source/recipes/plot_12_recipe.py
+++ b/docs/source/recipes/plot_12_recipe.py
@@ -13,8 +13,8 @@
 # %%
 # 1. Import cf-python, cf-plot and matplotlib.pyplot:
 
-import cfplot as cfp
 import matplotlib.pyplot as plt
+import cfplot as cfp
 
 import cf
 
diff --git a/docs/source/recipes/plot_13_recipe.py b/docs/source/recipes/plot_13_recipe.py
index 9b658597d8..bf0398713e 100644
--- a/docs/source/recipes/plot_13_recipe.py
+++ b/docs/source/recipes/plot_13_recipe.py
@@ -18,11 +18,13 @@
 # in next steps.
 
 import cartopy.crs as ccrs
-import cfplot as cfp
 import matplotlib.patches as mpatches
 
+import cfplot as cfp
+
 import cf
 
+
 # %%
 # 2. Read and select the SST by index and look at its contents:
 sst = cf.read("~/recipes/ERA5_monthly_averaged_SST.nc")[0]
diff --git a/docs/source/recipes/plot_17_recipe.py b/docs/source/recipes/plot_17_recipe.py
index a66c90b518..c94769e2ba 100644
--- a/docs/source/recipes/plot_17_recipe.py
+++ b/docs/source/recipes/plot_17_recipe.py
@@ -11,8 +11,8 @@
 # %%
 # 1. Import cf-python and cf-plot:
 
-import cfplot as cfp
 import matplotlib.pyplot as plt
+import cfplot as cfp
 
 import cf
 
diff --git a/docs/source/recipes/plot_18_recipe.py b/docs/source/recipes/plot_18_recipe.py
index 3beb9d0db9..f0eae36e35 100644
--- a/docs/source/recipes/plot_18_recipe.py
+++ b/docs/source/recipes/plot_18_recipe.py
@@ -10,15 +10,15 @@
 
 """
 
-import cfplot as cfp
-
 # %%
 # 1. Import cf-python, cf-plot and other required packages:
 import matplotlib.pyplot as plt
 import scipy.stats.mstats as mstats
+import cfplot as cfp
 
 import cf
 
+
 # %%
 # 2. Read the data in and unpack the Fields from FieldLists using indexing.
 # In our example We are investigating the influence of the land height on
diff --git a/docs/source/recipes/plot_19_recipe.py b/docs/source/recipes/plot_19_recipe.py
index ceb9db1c5c..dcc0926fbd 100644
--- a/docs/source/recipes/plot_19_recipe.py
+++ b/docs/source/recipes/plot_19_recipe.py
@@ -9,11 +9,10 @@
 maxima.
 """
 
-import cfplot as cfp
-
 # %%
 # 1. Import cf-python, cf-plot and other required packages:
 import matplotlib.pyplot as plt
+import cfplot as cfp
 
 import cf
 
@@ -56,10 +55,7 @@
 # of the maxima, we loop through the season query mapping and do a
 # "T: mean" collapse setting the season as the grouping:
 cfp.gopen(
-    rows=2,
-    columns=1,
-    bottom=0.1,
-    top=0.85,
+    rows=2, columns=1, bottom=0.1, top=0.85,
 )
 cfp.gpos(1)
 cfp.gset(xmin="1980-01-01", xmax="2022-12-01", ymin=304, ymax=312)
diff --git a/docs/source/recipes/recipe_list.txt b/docs/source/recipes/recipe_list.txt
index 0a8930811a..3dad79a79c 100644
--- a/docs/source/recipes/recipe_list.txt
+++ b/docs/source/recipes/recipe_list.txt
@@ -37,10 +37,4 @@ plot_18_recipe.html#sphx-glr-recipes-plot-18-recipe-py
 plot_19_recipe.html#sphx-glr-recipes-plot-19-recipe-py
 <div class="sphx-glr-thumbcontainer collapse subspace subplot lineplot" tooltip="Collapse, Subspace, Subplot, Lineplot">
 plot_20_recipe.html#sphx-glr-recipes-plot-20-recipe-py
-<div class="sphx-glr-thumbcontainer subspace contourmap vectorplot maths masking" tooltip="Subspace, Contourmap, Vectorplot, Mathematical Operations, Mask">
-plot_21_recipe.html#sphx-glr-recipes-plot-21-recipe-py
-<div class="sphx-glr-thumbcontainer maths stats" tooltip="Mathematical Operations, Statistical Operations">
-plot_22_recipe.html#sphx-glr-recipes-plot-22-recipe-py
-<div class="sphx-glr-thumbcontainer subspace maths" tooltip="Subspace, Mathematical Operations">
-plot_23_recipe.html#sphx-glr-recipes-plot-23-recipe-py
-<div class="sphx-glr-thumbcontainer subspace subplot vectorplot" tooltip="Subspace, Subplot, Vectorplot">
+<div class="sphx-glr-thumbcontainer subspace contourmap vectorplot maths masking" tooltip="Subspace, Contourmap, Vectorplot, Mathematical Operations, Mask">
\ No newline at end of file

From 238fd84ca61fb8de345d51bac85c0a0f57dc1496 Mon Sep 17 00:00:00 2001
From: David Hassell <davidhassell@users.noreply.github.com>
Date: Wed, 14 Jan 2026 13:27:07 +0000
Subject: [PATCH 06/10] Typos

Co-authored-by: Sadie L. Bartholomew <sadie.bartholomew@ncas.ac.uk>
---
 cf/read_write/read.py    | 2 +-
 docs/source/tutorial.rst | 2 +-
 setup.py                 | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/cf/read_write/read.py b/cf/read_write/read.py
index 803a4d8e39..52cc132e7e 100644
--- a/cf/read_write/read.py
+++ b/cf/read_write/read.py
@@ -334,7 +334,7 @@ class read(cfdm.read):
 
         {{read group_dimension_search: `str`, optional}}
 
-            .. versionadded:: (cfdm) NEXTVERSION
+            .. versionadded:: NEXTVERSION
 
         umversion: deprecated at version 3.0.0
             Use the *um* parameter instead.
diff --git a/docs/source/tutorial.rst b/docs/source/tutorial.rst
index 20cd5c11b6..a696524e8f 100644
--- a/docs/source/tutorial.rst
+++ b/docs/source/tutorial.rst
@@ -5348,7 +5348,7 @@ By default the output file will be for CF-|version|.
    
 The `cf.write` function has optional parameters to
 
-* set the output netCDF format (all netCDF3 and netCDF4 formats, as
+* set the output format (all netCDF3 and netCDF4 formats, as
   well as Zarr v3 are possible);
 
 * append to the netCDF file rather than over-writing it by default;
diff --git a/setup.py b/setup.py
index a9bdd9f268..2ed416976d 100755
--- a/setup.py
+++ b/setup.py
@@ -184,7 +184,7 @@ def compile():
 
 * create new field constructs in memory,
 
-* write and append field constructs and domain to netCDF and Zarr v3 datasets on disk,
+* write and append field and domain constructs to netCDF and Zarr v3 datasets on disk,
 
 * read, write, and create coordinates defined by geometry cells,
 

From 734ebfc5c34056084a49aeb492697fa8b71f3616 Mon Sep 17 00:00:00 2001
From: David Hassell <davidhassell@users.noreply.github.com>
Date: Wed, 14 Jan 2026 13:29:11 +0000
Subject: [PATCH 07/10] Remove duplicate info

Co-authored-by: Sadie L. Bartholomew <sadie.bartholomew@ncas.ac.uk>
---
 Changelog.rst | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Changelog.rst b/Changelog.rst
index ca1a0b96bd..7b134323e2 100644
--- a/Changelog.rst
+++ b/Changelog.rst
@@ -3,8 +3,7 @@ Version NEXTVERSION
 
 **2026-01-??**
 
-* Write Zarr v3 datasets with `cf.write`, and allow the reading of
-  grouped Zarr v2 and v3 datasets with `cf.read`
+* Write Zarr v3 datasets with `cf.write`
   (https://github.com/NCAS-CMS/cf-python/issues/895)
 * Read Zarr v2 and v3 datasets that contain a group hierarchy with
   `cf.read` (https://github.com/NCAS-CMS/cf-python/issues/894)

From 391d8ee2f2849253103711290447c0e1ce037c12 Mon Sep 17 00:00:00 2001
From: David Hassell <david.hassell@ncas.ac.uk>
Date: Wed, 14 Jan 2026 13:30:23 +0000
Subject: [PATCH 08/10] revert bad linting

---
 docs/source/recipes/plot_19_recipe.py | 5 ++++-
 docs/source/recipes/plot_22_recipe.py | 5 ++---
 docs/source/recipes/plot_23_recipe.py | 8 ++++----
 docs/source/recipes/recipe_list.txt   | 8 +++++++-
 4 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/docs/source/recipes/plot_19_recipe.py b/docs/source/recipes/plot_19_recipe.py
index dcc0926fbd..02d493dc21 100644
--- a/docs/source/recipes/plot_19_recipe.py
+++ b/docs/source/recipes/plot_19_recipe.py
@@ -55,7 +55,10 @@
 # of the maxima, we loop through the season query mapping and do a
 # "T: mean" collapse setting the season as the grouping:
 cfp.gopen(
-    rows=2, columns=1, bottom=0.1, top=0.85,
+    rows=2,
+    columns=1,
+    bottom=0.1,
+    top=0.85,
 )
 cfp.gpos(1)
 cfp.gset(xmin="1980-01-01", xmax="2022-12-01", ymin=304, ymax=312)
diff --git a/docs/source/recipes/plot_22_recipe.py b/docs/source/recipes/plot_22_recipe.py
index fe329cda9d..377313c899 100644
--- a/docs/source/recipes/plot_22_recipe.py
+++ b/docs/source/recipes/plot_22_recipe.py
@@ -11,11 +11,10 @@
 # %%
 # 1. Import cf-python, Dask.array, NumPy, and Matplotlib:
 
+import cf
 import dask.array as da
-import matplotlib.pyplot as plt
 import numpy as np
-
-import cf
+import matplotlib.pyplot as plt
 
 # %%
 # 2. Read the field constructs and load the wind speed component fields:
diff --git a/docs/source/recipes/plot_23_recipe.py b/docs/source/recipes/plot_23_recipe.py
index 29537803af..2499b0d875 100644
--- a/docs/source/recipes/plot_23_recipe.py
+++ b/docs/source/recipes/plot_23_recipe.py
@@ -18,13 +18,13 @@
 # sphinx_gallery_thumbnail_number = 2
 # sphinx_gallery_end_ignore
 
-import cfplot as cfp
-import dask.array as da
 import matplotlib.pyplot as plt
-import numpy as np
-
+import cfplot as cfp
 import cf
 
+import numpy as np
+import dask.array as da
+
 # %%
 # 2. Read example data field constructs, and set region for our plots:
 
diff --git a/docs/source/recipes/recipe_list.txt b/docs/source/recipes/recipe_list.txt
index 3dad79a79c..0a8930811a 100644
--- a/docs/source/recipes/recipe_list.txt
+++ b/docs/source/recipes/recipe_list.txt
@@ -37,4 +37,10 @@ plot_18_recipe.html#sphx-glr-recipes-plot-18-recipe-py
 plot_19_recipe.html#sphx-glr-recipes-plot-19-recipe-py
 <div class="sphx-glr-thumbcontainer collapse subspace subplot lineplot" tooltip="Collapse, Subspace, Subplot, Lineplot">
 plot_20_recipe.html#sphx-glr-recipes-plot-20-recipe-py
-<div class="sphx-glr-thumbcontainer subspace contourmap vectorplot maths masking" tooltip="Subspace, Contourmap, Vectorplot, Mathematical Operations, Mask">
\ No newline at end of file
+<div class="sphx-glr-thumbcontainer subspace contourmap vectorplot maths masking" tooltip="Subspace, Contourmap, Vectorplot, Mathematical Operations, Mask">
+plot_21_recipe.html#sphx-glr-recipes-plot-21-recipe-py
+<div class="sphx-glr-thumbcontainer maths stats" tooltip="Mathematical Operations, Statistical Operations">
+plot_22_recipe.html#sphx-glr-recipes-plot-22-recipe-py
+<div class="sphx-glr-thumbcontainer subspace maths" tooltip="Subspace, Mathematical Operations">
+plot_23_recipe.html#sphx-glr-recipes-plot-23-recipe-py
+<div class="sphx-glr-thumbcontainer subspace subplot vectorplot" tooltip="Subspace, Subplot, Vectorplot">

From 8d6ff49c760e90d86503e20018dd388ed837e090 Mon Sep 17 00:00:00 2001
From: David Hassell <david.hassell@ncas.ac.uk>
Date: Wed, 14 Jan 2026 13:54:32 +0000
Subject: [PATCH 09/10] _get_cached_elements -> get_cached_elements

---
 cf/aggregate.py           |  2 +-
 cf/dimensioncoordinate.py |  4 +-
 cf/field.py               |  2 +-
 cf/test/test_Data.py      | 81 +++++++++++++--------------------------
 4 files changed, 31 insertions(+), 58 deletions(-)

diff --git a/cf/aggregate.py b/cf/aggregate.py
index ff53f31aa3..149be58d67 100644
--- a/cf/aggregate.py
+++ b/cf/aggregate.py
@@ -4112,7 +4112,7 @@ def _get_hfl(
         # Record the bounds of the first and last (sorted) cells
         first, last = hfl_cache.flb.get(hash_value, (None, None))
         if first is None:
-            cached_elements = d._get_cached_elements()
+            cached_elements = d.get_cached_elements()
             x = []
             for i in (0, 1, -2, -1):
                 value = cached_elements.get(i)
diff --git a/cf/dimensioncoordinate.py b/cf/dimensioncoordinate.py
index 644709bbda..c1a061e55f 100644
--- a/cf/dimensioncoordinate.py
+++ b/cf/dimensioncoordinate.py
@@ -165,7 +165,7 @@ def _infer_direction(self):
         if data is not None:
             # Infer the direction from the data
             if data.size > 1:
-                c = data._get_cached_elements()
+                c = data.get_cached_elements()
                 if c:
                     try:
                         return bool(c.get(0) <= c.get(1))
@@ -179,7 +179,7 @@ def _infer_direction(self):
         data = self.get_bounds_data(None, _fill_value=False)
         if data is not None:
             # Infer the direction from the bounds
-            c = data._get_cached_elements()
+            c = data.get_cached_elements()
             if c:
                 try:
                     return bool(c.get(0) <= c.get(1))
diff --git a/cf/field.py b/cf/field.py
index 53b889259d..b571158ea9 100644
--- a/cf/field.py
+++ b/cf/field.py
@@ -6994,7 +6994,7 @@ def collapse(
                 else:
                     b = dim.data
 
-                cached_elements = b._get_cached_elements()
+                cached_elements = b.get_cached_elements()
                 try:
                     # Try to set the new bounds from cached values
                     bounds_data = Data(
diff --git a/cf/test/test_Data.py b/cf/test/test_Data.py
index 2300a62e47..15d67c894b 100644
--- a/cf/test/test_Data.py
+++ b/cf/test/test_Data.py
@@ -1165,7 +1165,7 @@ def test_Data_concatenate(self):
         str(d)
         str(e)
         f = cf.Data.concatenate([d, e], axis=1)
-        cached = f._get_cached_elements()
+        cached = f.get_cached_elements()
         self.assertEqual(cached[0], d.first_element())
         self.assertEqual(cached[-1], e.last_element())
 
@@ -1205,7 +1205,7 @@ def test_Data_concatenate(self):
         repr(e)
         f = cf.Data.concatenate([d, e], axis=0)
         self.assertEqual(
-            f._get_cached_elements(),
+            f.get_cached_elements(),
             {0: d.first_element(), -1: e.last_element()},
         )
 
@@ -4378,7 +4378,7 @@ def test_Data_Units(self):
         d = cf.Data([1000, 2000, 3000], "m")
         repr(d)
         d.Units = cf.Units("km")
-        self.assertEqual(d._get_cached_elements(), {0: 1.0, 1: 2.0, -1: 3.0})
+        self.assertEqual(d.get_cached_elements(), {0: 1.0, 1: 2.0, -1: 3.0})
 
     def test_Data_get_data(self):
         """Test the `get_data` Data method."""
@@ -4446,57 +4446,30 @@ def test_Data__init__datetime(self):
         self.assertTrue((q == d).array.all())
         self.assertTrue((d == q).array.all())
 
-    def test_Data__str__(self):
-        """Test `Data.__str__`"""
-        elements0 = (0, -1, 1)
-        for array in ([1], [1, 2], [1, 2, 3]):
-            elements = elements0[: len(array)]
-
-            d = cf.Data(array)
-            cache = d._get_cached_elements()
-            for element in elements:
-                self.assertNotIn(element, cache)
-
-            self.assertEqual(str(d), str(array))
-            cache = d._get_cached_elements()
-            for element in elements:
-                self.assertIn(element, cache)
-
-            d[0] = 1
-            cache = d._get_cached_elements()
-            for element in elements:
-                self.assertNotIn(element, cache)
-
-            self.assertEqual(str(d), str(array))
-            cache = d._get_cached_elements()
-            for element in elements:
-                self.assertIn(element, cache)
-
-            d += 0
-            cache = d._get_cached_elements()
-            for element in elements:
-                self.assertNotIn(element, cache)
-
-            self.assertEqual(str(d), str(array))
-            cache = d._get_cached_elements()
-            for element in elements:
-                self.assertIn(element, cache)
-
-        # Test when size > 3, i.e. second element is not there.
-        d = cf.Data([1, 2, 3, 4])
-        cache = d._get_cached_elements()
-        for element in elements0:
-            self.assertNotIn(element, cache)
-
-        self.assertEqual(str(d), "[1, ..., 4]")
-        cache = d._get_cached_elements()
-        self.assertNotIn(1, cache)
-        for element in elements0[:2]:
-            self.assertIn(element, cache)
-
-        d[0] = 1
-        for element in elements0:
-            self.assertNotIn(element, d._get_cached_elements())
+    def test_Data__repr__str(self):
+        """Test all means of Data inspection."""
+        for d in [
+            cf.Data(9, units="km"),
+            cf.Data([9], units="km"),
+            cf.Data([[9]], units="km"),
+            cf.Data([8, 9], units="km"),
+            cf.Data([[8, 9]], units="km"),
+            cf.Data([7, 8, 9], units="km"),
+            cf.Data([[7, 8, 9]], units="km"),
+            cf.Data([6, 7, 8, 9], units="km"),
+            cf.Data([[6, 7, 8, 9]], units="km"),
+            cf.Data([[6, 7], [8, 9]], units="km"),
+            cf.Data([[6, 7, 8, 9], [6, 7, 8, 9]], units="km"),
+        ]:
+            _ = repr(d)
+            _ = str(d)
+
+        # Test when the data contains date-times with the first
+        # element masked
+        dt = np.ma.array([10, 20], mask=[True, False])
+        d = cf.Data(dt, units="days since 2000-01-01")
+        self.assertTrue(str(d) == "[--, 2000-01-21 00:00:00]")
+        self.assertTrue(repr(d) == "<CF Data(2): [--, 2000-01-21 00:00:00]>")
 
     def test_Data_cull_graph(self):
         """Test Data.cull_graph."""

From 30ad381dab381a67f96155900f771b650cf59b13 Mon Sep 17 00:00:00 2001
From: David Hassell <david.hassell@ncas.ac.uk>
Date: Wed, 14 Jan 2026 13:54:41 +0000
Subject: [PATCH 10/10] _get_cached_elements -> get_cached_elements

---
 cf/data/data.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cf/data/data.py b/cf/data/data.py
index e906087c93..7b75d16008 100644
--- a/cf/data/data.py
+++ b/cf/data/data.py
@@ -2761,7 +2761,7 @@ def Units(self, value):
             self._set_dask(dx, clear=self._ALL ^ self._CACHE ^ self._CFA)
 
             # Adjust cached values for the new units
-            cache = self._get_cached_elements()
+            cache = self.get_cached_elements()
             if cache:
                 self._set_cached_elements(
                     {index: cf_func(value) for index, value in cache.items()}