Merge pull request #4316 from chrishavlin/fix_unit_system_name_reload

Closes #4315

nose_unit.cfg

@@ -6,5 +6,5 @@ nologcapture=1
 verbosity=2
 where=yt
 with-timer=1
-ignore-files=(test_load_errors.py|test_load_sample.py|test_commons.py|test_ambiguous_fields.py|test_field_access_pytest.py|test_save.py|test_line_annotation_unit.py|test_eps_writer.py|test_registration.py|test_invalid_origin.py|test_outputs_pytest\.py|test_normal_plot_api\.py|test_load_archive\.py|test_stream_particles\.py|test_file_sanitizer\.py|test_version\.py|\test_on_demand_imports\.py|test_set_zlim\.py|test_add_field\.py|test_glue\.py|test_geometries\.py|test_firefly\.py|test_callable_grids\.py|test_external_frontends\.py|test_stream_stretched\.py|test_sanitize_center\.py)
+ignore-files=(test_load_errors.py|test_load_sample.py|test_commons.py|test_ambiguous_fields.py|test_field_access_pytest.py|test_save.py|test_line_annotation_unit.py|test_eps_writer.py|test_registration.py|test_invalid_origin.py|test_outputs_pytest\.py|test_normal_plot_api\.py|test_load_archive\.py|test_stream_particles\.py|test_file_sanitizer\.py|test_version\.py|\test_on_demand_imports\.py|test_set_zlim\.py|test_add_field\.py|test_glue\.py|test_geometries\.py|test_firefly\.py|test_callable_grids\.py|test_external_frontends\.py|test_stream_stretched\.py|test_sanitize_center\.py|test_data_reload\.py)
 exclude-test=yt.frontends.gdf.tests.test_outputs.TestGDF

tests/tests.yaml

@@ -230,6 +230,7 @@ other_tests:
      - "--ignore-file=test_firefly\\.py"
      - "--ignore-file=test_callable_grids\\.py"
      - "--ignore-file=test_external_frontends\\.py"
+     - "--ignore-file=test_data_reload\\.py"
      - "--ignore-file=test_stream_stretched\\.py"
      - "--ignore-files=test_sanitize_center\\.py"
      - "--exclude-test=yt.frontends.gdf.tests.test_outputs.TestGDF"

yt/frontends/ytdata/tests/test_data_reload.py

@@ -0,0 +1,26 @@
+import numpy as np
+
+from yt.loaders import load_uniform_grid
+from yt.testing import requires_module_pytest
+from yt.utilities.on_demand_imports import _h5py as h5py
+
+
+@requires_module_pytest("h5py")
+def test_save_as_data_unit_system(tmp_path):
+    # This test checks that the file saved with calling save_as_dataset
+    # for a ds with a "code" unit system contains the proper "unit_system_name".
+    # It checks the hdf5 file directly rather than using yt.load(), because
+    # https://github.com/yt-project/yt/issues/4315 only manifested restarting
+    # the python kernel (because the unit registry is state dependent).
+
+    fi = tmp_path / "output_data.h5"
+    shp = (4, 4, 4)
+    data = {"density": np.random.random(shp)}
+    ds = load_uniform_grid(data, shp, unit_system="code")
+    assert "code" in ds._unit_system_name
+
+    sp = ds.sphere(ds.domain_center, ds.domain_width[0] / 2.0)
+    sp.save_as_dataset(fi)
+
+    with h5py.File(fi, mode="r") as f:
+        assert f.attrs["unit_system_name"] == "code"

yt/frontends/ytdata/utilities.py

@@ -103,7 +103,12 @@ def save_as_dataset(ds, filename, data, field_types=None, extra_attrs=None):
         _yt_array_hdf5_attr(fh, "unit_registry_json", ds.unit_registry.to_json())
 
     if hasattr(ds, "unit_system"):
-        _yt_array_hdf5_attr(fh, "unit_system_name", ds.unit_system.name.split("_")[0])
+        # Note: ds._unit_system_name is written here rather than
+        # ds.unit_system.name because for a 'code' unit system, ds.unit_system.name
+        # is a hash, not a unit system. And on re-load, we want to designate
+        # a unit system not a hash value.
+        # See https://github.com/yt-project/yt/issues/4315 for more background.
+        _yt_array_hdf5_attr(fh, "unit_system_name", ds._unit_system_name)
 
     for attr in base_attrs:
         if isinstance(ds, dict):