Persist data after computation

Changelog.rst

@@ -3,6 +3,10 @@ Version NEXTVERSION
 
 **2026-??-??**
 
+* New keyword parameter to `cf.Data.compute`: ``persist``
+  (https://github.com/NCAS-CMS/cf-python/issues/929)
+* New function to control the persistence of computed data:
+  `cf.persist_data` (https://github.com/NCAS-CMS/cf-python/issues/929)
 * New default backend for netCDF-4 in `cf.write`: ``h5netcdf-h5py``,
   that allows control of the internal file metadata via the new
   ``h5py_options`` parameter

cf/functions.py

@@ -157,6 +157,7 @@ def configuration(
     chunksize=None,
     log_level=None,
     display_data=None,
+    persist_data=None,
     regrid_logging=None,
     relaxed_identities=None,
     bounds_combination_mode=None,
@@ -179,6 +180,7 @@ def configuration(
     * `chunksize`
     * `log_level`
     * `display_data`
+    * `persist_data`
     * `regrid_logging`
     * `relaxed_identities`
     * `bounds_combination_mode`
@@ -203,9 +205,10 @@ def configuration(
 
     .. seealso:: `atol`, `rtol`, `tempdir`, `chunksize`,
                  `total_memory`, `log_level`, `display_data`,
-                 `regrid_logging`, `relaxed_identities`,
-                 `bounds_combination_mode`, `active_storage`,
-                 `active_storage_url`, `active_storage_max_requests`
+                 `persist_data`, `regrid_logging`,
+                 `relaxed_identities`, `bounds_combination_mode`,
+                 `active_storage`, `active_storage_url`,
+                 `active_storage_max_requests`
 
     :Parameters:
 
@@ -247,12 +250,18 @@ def configuration(
             * ``'DETAIL'`` (``3``);
             * ``'DEBUG'`` (``-1``).
 
-        display_data `bool` or `Constant`, optional
+        display_data: `bool` or `Constant`, optional
             The new display data option. The default is to not change
             the current behaviour.
 
             .. versionadded:: 3.19.0
 
+        persist_data: `bool` or `Constant`, optional
+            The new persist data option. The default is to not change
+            the current behaviour.
+
+            .. versionadded:: NEXTVERSION
+
         regrid_logging: `bool` or `Constant`, optional
             The new value (either True to enable logging or False to
             disable it). The default is to not change the current
@@ -312,6 +321,7 @@ def configuration(
      'bounds_combination_mode': 'AND',
      'chunksize': 82873466.88000001,
      'display_data': True,
+     'persist_data': False,
      'active_storage': False,
      'active_storage_url': None,
      'active_storage_max_requests': 100}
@@ -330,6 +340,7 @@ def configuration(
      'bounds_combination_mode': 'AND',
      'chunksize': 75000000.0,
      'display_data': True,
+     'persist_data': False,
      'active_storage': False,
      'active_storage_url': None,
      'active_storage_max_requests': 100}
@@ -358,6 +369,7 @@ def configuration(
      'bounds_combination_mode': 'AND',
      'chunksize': 75000000.0,
      'display_data': True,
+     'persist_data': False,
      'active_storage': False,
      'active_storage_url': None}
     >>> with cf.configuration(atol=9, rtol=10):
@@ -372,6 +384,7 @@ def configuration(
      'bounds_combination_mode': 'AND',
      'chunksize': 75000000.0,
      'display_data': True,
+     'persist_data': False,
      'active_storage': False,
      'active_storage_url': None,
      'active_storage_max_requests': 100}
@@ -385,6 +398,7 @@ def configuration(
      'bounds_combination_mode': 'AND',
      'chunksize': 75000000.0,
      'display_data': True,
+     'persist_data': False,
      'active_storage': False,
      'active_storage_url': None,
      'active_storage_max_requests': 100}
@@ -416,6 +430,7 @@ def configuration(
         new_chunksize=chunksize,
         new_log_level=log_level,
         new_display_data=display_data,
+        new_persist_data=persist_data,
         new_regrid_logging=regrid_logging,
         new_relaxed_identities=relaxed_identities,
         bounds_combination_mode=bounds_combination_mode,
@@ -460,6 +475,7 @@ def _configuration(_Configuration, **kwargs):
         "new_chunksize": chunksize,
         "new_log_level": log_level,
         "new_display_data": display_data,
+        "new_persist_data": persist_data,
         "new_regrid_logging": regrid_logging,
         "new_relaxed_identities": relaxed_identities,
         "bounds_combination_mode": bounds_combination_mode,
@@ -590,6 +606,10 @@ class display_data(ConstantAccess, cfdm.display_data):
     pass
 
 
+class persist_data(ConstantAccess, cfdm.persist_data):
+    pass
+
+
 class regrid_logging(ConstantAccess):
     """Whether or not to enable `esmpy` regridding logging.
 

cf/test/test_Data.py

@@ -17,6 +17,8 @@
 
 faulthandler.enable()  # to debug seg faults and timeouts
 
+import cfdm
+
 import cf
 
 n_tmpfiles = 2
@@ -3050,8 +3052,6 @@ def test_Data_where(self):
 
     def test_Data__init__compression(self):
         """Test Data initialised from compressed data sources."""
-        import cfdm
-
         # Ragged
         for f in cfdm.read("DSG_timeSeries_contiguous.nc"):
             f = f.data
@@ -3200,6 +3200,59 @@ def test_Data_compute(self):
         d.compute()
         self.assertEqual(d.get_cached_elements(), {0: 1, 1: 2, -1: 2})
 
+        # Persist
+        f = cf.read(self.filename, dask_chunks=3)[0]
+        d0 = f.data
+        npartitions = d0.npartitions
+        self.assertGreater(npartitions, 1)
+
+        with cf.persist_data(False):
+            d = d0.copy()
+            a = d.compute()
+            self.assertEqual(len(d.get_filenames()), 1)
+            b = d.compute()
+            self.assertEqual(len(d.get_filenames()), 1)
+            self.assertTrue(np.allclose(a, b))
+
+            d = d0.copy()
+            a = d.compute()
+            self.assertEqual(len(d.get_filenames()), 1)
+            b = d.compute(persist=None)
+            self.assertEqual(len(d.get_filenames()), 1)
+            self.assertTrue(np.allclose(a, b))
+
+            d = d0.copy()
+            a = d.compute()
+            self.assertEqual(len(d.get_filenames()), 1)
+            b = d.compute(persist=False)
+            self.assertEqual(len(d.get_filenames()), 1)
+            self.assertTrue(np.allclose(a, b))
+
+            d = d0.copy()
+            a = d.compute()
+            self.assertEqual(len(d.get_filenames()), 1)
+            b = d.compute(persist=True)
+            self.assertEqual(len(d.get_filenames()), 0)
+            self.assertEqual(d.npartitions, npartitions)
+            self.assertTrue(np.allclose(a, b))
+
+        with cf.persist_data(True):
+            d = d0.copy()
+            d.compute()
+            self.assertEqual(len(d.get_filenames()), 0)
+
+            d = d0.copy()
+            d.compute(persist=None)
+            self.assertEqual(len(d.get_filenames()), 0)
+
+            d = d0.copy()
+            d.compute(persist=False)
+            self.assertEqual(len(d.get_filenames()), 1)
+
+            d = d0.copy()
+            d.compute(persist=True)
+            self.assertEqual(len(d.get_filenames()), 0)
+
     def test_Data_persist(self):
         """Test Data.persist."""
         d = cf.Data(9, "km")
@@ -4149,8 +4202,6 @@ def test_Data_masked_invalid(self):
 
     def test_Data_uncompress(self):
         """Test the `uncompress` Data method."""
-        import cfdm
-
         f = cfdm.read("DSG_timeSeries_contiguous.nc")[0]
         a = f.data.array
         d = cf.Data(cf.RaggedContiguousArray(source=f.data.source()))
@@ -4274,8 +4325,6 @@ def test_Data_soften_mask(self):
 
     def test_Data_compressed_array(self):
         """Test the `compressed_array` Data property."""
-        import cfdm
-
         f = cfdm.read("DSG_timeSeries_contiguous.nc")[0]
         f = f.data
         d = cf.Data(cf.RaggedContiguousArray(source=f.source()))
@@ -4305,8 +4354,6 @@ def test_Data_fits_in_memory(self):
 
     def test_Data_get_compressed(self):
         """Test the Data methods which get compression properties."""
-        import cfdm
-
         # Compressed
         f = cfdm.read("DSG_timeSeries_contiguous.nc")[0]
         f = f.data
@@ -4365,8 +4412,6 @@ def test_Data_get_data(self):
 
     def test_Data_get_count(self):
         """Test the `get_count` Data method."""
-        import cfdm
-
         f = cfdm.read("DSG_timeSeries_contiguous.nc")[0]
         f = f.data
         d = cf.Data(cf.RaggedContiguousArray(source=f.source()))
@@ -4378,8 +4423,6 @@ def test_Data_get_count(self):
 
     def test_Data_get_index(self):
         """Test the `get_index` Data method."""
-        import cfdm
-
         f = cfdm.read("DSG_timeSeries_indexed.nc")[0]
         f = f.data
         d = cf.Data(cf.RaggedIndexedArray(source=f.source()))
@@ -4391,8 +4434,6 @@ def test_Data_get_index(self):
 
     def test_Data_get_list(self):
         """Test the `get_list` Data method."""
-        import cfdm
-
         f = cfdm.read("gathered.nc")[0]
         f = f.data
         d = cf.Data(cf.GatheredArray(source=f.source()))

cf/test/test_functions.py

@@ -55,7 +55,7 @@ def test_configuration(self):
         self.assertIsInstance(org, dict)
 
         # Check all keys that should be there are, with correct value type:
-        self.assertEqual(len(org), 12)  # update expected len if add new key(s)
+        self.assertEqual(len(org), 13)  # update expected len if add new key(s)
 
         # Types expected:
         self.assertIsInstance(org["atol"], float)
@@ -71,6 +71,7 @@ def test_configuration(self):
         # equiv. string
         self.assertIsInstance(org["log_level"], str)
         self.assertIsInstance(org["display_data"], bool)
+        self.assertIsInstance(org["persist_data"], bool)
 
         # Store some sensible values to reset items to for testing, ensuring:
         # 1) they are kept different to the defaults (i.e. org values); and

docs/source/function.rst

@@ -135,6 +135,8 @@ Resource management
 
    cf.configuration
    cf.chunksize
+   cf.display_data
+   cf.persist_data
    cf.free_memory
    cf.regrid_logging
    cf.tempdir