Add support for NETCDF3_64BIT_DATA in write_netcdf()

conda_package/dev-spec.txt

@@ -12,6 +12,7 @@ hdf5
 inpoly
 libnetcdf
 matplotlib-base>=3.9.0
+nco
 netcdf4
 networkx
 numpy>=2.0,<3.0

conda_package/docs/index.rst

@@ -27,6 +27,8 @@ analyzing simulations, and in other MPAS-related workflows.
 
    config
 
+   io
+
    logging
 
    transects

conda_package/docs/io.rst

@@ -0,0 +1,28 @@
+.. _io:
+
+*********
+I/O Tools
+*********
+
+The :py:mod:`mpas_tools.io` module provides utilities for reading and writing
+NetCDF files, especially for compatibility with MPAS mesh and data conventions.
+
+write_netcdf
+============
+
+The :py:func:`mpas_tools.io.write_netcdf()` function writes an
+``xarray.Dataset`` to a NetCDF file, ensuring MPAS compatibility (e.g.,
+converting int64 to int32, handling fill values, and updating the history
+attribute). It also supports writing in various NetCDF formats, including
+conversion to ``NETCDF3_64BIT_DATA`` using ``ncks`` if needed.
+
+Example usage:
+
+.. code-block:: python
+
+    import xarray as xr
+    from mpas_tools.io import write_netcdf
+
+    # Create a simple dataset
+    ds = xr.Dataset({'foo': (('x',), [1, 2, 3])})
+    write_netcdf(ds, 'output.nc')

conda_package/mpas_tools/io.py

@@ -1,25 +1,43 @@
-from __future__ import absolute_import, division, print_function, \
-    unicode_literals
+import os
+import subprocess
+import sys
+from datetime import datetime
+from pathlib import Path
 
-import numpy
 import netCDF4
-from datetime import datetime
-import sys
+import numpy
 
+from mpas_tools.logging import check_call
 
 default_format = 'NETCDF3_64BIT'
 default_engine = None
 default_char_dim_name = 'StrLen'
 default_fills = netCDF4.default_fillvals
 
 
-def write_netcdf(ds, fileName, fillValues=None, format=None, engine=None,
-                 char_dim_name=None):
+def write_netcdf(
+    ds,
+    fileName,
+    fillValues=None,
+    format=None,
+    engine=None,
+    char_dim_name=None,
+    logger=None,
+):
     """
     Write an xarray.Dataset to a file with NetCDF4 fill values and the given
     name of the string dimension.  Also adds the time and command-line to the
     history attribute.
 
+    Note: the ``NETCDF3_64BIT_DATA`` format is handled as a special case
+    because xarray output with this format is not performant. First, the file
+    is written in `NETCDF4` format, which supports larger files and variables.
+    Then, the `ncks` command is used to convert the file to the
+    `NETCDF3_64BIT_DATA` format.
+
+    Note: All int64 variables are automatically converted to int32 for MPAS
+    compatibility.
+
     Parameters
     ----------
     ds : xarray.Dataset
@@ -50,7 +68,11 @@ def write_netcdf(ds, fileName, fillValues=None, format=None, engine=None,
         ``mpas_tools.io.default_char_dim_name``, which can be modified but
         which defaults to ``'StrLen'``
 
-    """
+    logger : logging.Logger, optional
+        A logger to write messages to write the output of `ncks` conversion
+        calls to.  If None, `ncks` output is suppressed.  This is only
+        relevant if `format` is 'NETCDF3_64BIT_DATA'
+    """  # noqa: E501
     if format is None:
         format = default_format
 
@@ -63,6 +85,13 @@ def write_netcdf(ds, fileName, fillValues=None, format=None, engine=None,
     if char_dim_name is None:
         char_dim_name = default_char_dim_name
 
+    # Convert int64 variables to int32 for MPAS compatibility
+    for var in list(ds.data_vars.keys()) + list(ds.coords.keys()):
+        if ds[var].dtype == numpy.int64:
+            attrs = ds[var].attrs.copy()
+            ds[var] = ds[var].astype(numpy.int32)
+            ds[var].attrs = attrs
+
     encodingDict = {}
     variableNames = list(ds.data_vars.keys()) + list(ds.coords.keys())
     for variableName in variableNames:
@@ -71,8 +100,9 @@ def write_netcdf(ds, fileName, fillValues=None, format=None, engine=None,
             dtype = ds[variableName].dtype
             for fillType in fillValues:
                 if dtype == numpy.dtype(fillType):
-                    encodingDict[variableName] = \
-                        {'_FillValue': fillValues[fillType]}
+                    encodingDict[variableName] = {
+                        '_FillValue': fillValues[fillType]
+                    }
                     break
         else:
             encodingDict[variableName] = {'_FillValue': None}
@@ -88,14 +118,54 @@ def write_netcdf(ds, fileName, fillValues=None, format=None, engine=None,
         # reading Time otherwise
         ds.encoding['unlimited_dims'] = {'Time'}
 
-    ds.to_netcdf(fileName, encoding=encodingDict, format=format, engine=engine)
+    # for performance, we have to handle this as a special case
+    convert = format == 'NETCDF3_64BIT_DATA'
+
+    if convert:
+        out_path = Path(fileName)
+        out_filename = (
+            out_path.parent / f'_tmp_{out_path.stem}.netcdf4{out_path.suffix}'
+        )
+        format = 'NETCDF4'
+        if engine == 'scipy':
+            # that's not going to work
+            engine = 'netcdf4'
+    else:
+        out_filename = fileName
+
+    ds.to_netcdf(
+        out_filename, encoding=encodingDict, format=format, engine=engine
+    )
+
+    if convert:
+        args = [
+            'ncks',
+            '-O',
+            '-5',
+            out_filename,
+            fileName,
+        ]
+        if logger is None:
+            subprocess.run(
+                args,
+                check=True,
+                stdout=subprocess.DEVNULL,
+                stderr=subprocess.DEVNULL,
+            )
+        else:
+            check_call(args, logger=logger)
+        # delete the temporary NETCDF4 file
+        os.remove(out_filename)
 
 
 def update_history(ds):
-    '''Add or append history to attributes of a data set'''
+    """Add or append history to attributes of a data set"""
 
-    thiscommand = datetime.now().strftime("%a %b %d %H:%M:%S %Y") + ": " + \
-        " ".join(sys.argv[:])
+    thiscommand = (
+        datetime.now().strftime('%a %b %d %H:%M:%S %Y')
+        + ': '
+        + ' '.join(sys.argv[:])
+    )
     if 'history' in ds.attrs:
         newhist = '\n'.join([thiscommand, ds.attrs['history']])
     else:

conda_package/mpas_tools/mesh/mask.py

@@ -251,9 +251,13 @@ def entry_point_compute_mpas_region_masks():
             subdivisionThreshold=args.subdivision,
         )
 
-    write_netcdf(
-        dsMasks, args.mask_file_name, format=args.format, engine=args.engine
-    )
+        write_netcdf(
+            dsMasks,
+            args.mask_file_name,
+            format=args.format,
+            engine=args.engine,
+            logger=logger,
+        )
 
 
 def compute_mpas_transect_masks(
@@ -516,9 +520,13 @@ def entry_point_compute_mpas_transect_masks():
             addEdgeSign=args.add_edge_sign,
         )
 
-    write_netcdf(
-        dsMasks, args.mask_file_name, format=args.format, engine=args.engine
-    )
+        write_netcdf(
+            dsMasks,
+            args.mask_file_name,
+            format=args.format,
+            engine=args.engine,
+            logger=logger,
+        )
 
 
 def compute_mpas_flood_fill_mask(
@@ -641,9 +649,13 @@ def entry_point_compute_mpas_flood_fill_mask():
             dsMesh=dsMesh, fcSeed=fcSeed, logger=logger
         )
 
-    write_netcdf(
-        dsMasks, args.mask_file_name, format=args.format, engine=args.engine
-    )
+        write_netcdf(
+            dsMasks,
+            args.mask_file_name,
+            format=args.format,
+            engine=args.engine,
+            logger=logger,
+        )
 
 
 def compute_lon_lat_region_masks(
@@ -868,7 +880,11 @@ def entry_point_compute_lon_lat_region_masks():
         )
 
     write_netcdf(
-        dsMasks, args.mask_file_name, format=args.format, engine=args.engine
+        dsMasks,
+        args.mask_file_name,
+        format=args.format,
+        engine=args.engine,
+        logger=logger,
     )
 
 
@@ -1101,7 +1117,11 @@ def entry_point_compute_projection_grid_region_masks():
         )
 
     write_netcdf(
-        dsMasks, args.mask_file_name, format=args.format, engine=args.engine
+        dsMasks,
+        args.mask_file_name,
+        format=args.format,
+        engine=args.engine,
+        logger=logger,
     )
 
 

conda_package/recipe/meta.yaml

@@ -42,6 +42,7 @@ requirements:
     - networkx
     - netcdf-fortran
     - matplotlib-base >=3.9.0
+    - nco
     - netcdf4
     - numpy >=2.0,<3.0
     - progressbar2

conda_package/tests/test_io.py

@@ -0,0 +1,102 @@
+import os
+import subprocess
+
+import numpy as np
+import pytest
+import xarray as xr
+
+from mpas_tools.io import write_netcdf
+
+from .util import get_test_data_file
+
+TEST_MESH = get_test_data_file('mesh.QU.1920km.151026.nc')
+
+
+@pytest.mark.skipif(
+    not os.path.exists(TEST_MESH), reason='Test mesh not available'
+)
+def test_write_netcdf_basic(tmp_path):
+    ds = xr.open_dataset(TEST_MESH)
+    out_file = tmp_path / 'test_basic.nc'
+    write_netcdf(ds, str(out_file))
+    ds2 = xr.open_dataset(out_file)
+    # Should have same dimensions and variables
+    assert set(ds.dims) == set(ds2.dims)
+    for var in ds.data_vars:
+        assert var in ds2.data_vars
+    ds2.close()
+
+
+@pytest.mark.skipif(
+    not os.path.exists(TEST_MESH), reason='Test mesh not available'
+)
+def test_write_netcdf_cdf5_format(tmp_path):
+    ds = xr.open_dataset(TEST_MESH)
+    out_file = tmp_path / 'test_cdf5.nc'
+    write_netcdf(ds, str(out_file), format='NETCDF3_64BIT_DATA')
+    # Use ncdump -k to check format
+    result = subprocess.run(
+        ['ncdump', '-k', str(out_file)],
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    # Should be cdf5 for NETCDF3_64BIT_DATA
+    assert result.stdout.strip() == 'cdf5'
+    # Check that the temporary file was deleted
+    tmp_file = (
+        out_file.parent / f'_tmp_{out_file.stem}.netcdf4{out_file.suffix}'
+    )
+    assert not os.path.exists(tmp_file)
+
+
+def test_write_netcdf_int64_conversion_and_attr(tmp_path):
+    # Create a dataset with int64 variable and an attribute
+    arr = np.array([1, 2, 3], dtype=np.int64)
+    ds = xr.Dataset({'foo': (('x',), arr)})
+    ds['foo'].attrs['myattr'] = 'testattr'
+    out_file = tmp_path / 'test_int64.nc'
+    write_netcdf(ds, str(out_file))
+    ds2 = xr.open_dataset(out_file)
+    # Should be int32, not int64
+    assert ds2['foo'].dtype == np.int32
+    # Attribute should be preserved
+    assert ds2['foo'].attrs['myattr'] == 'testattr'
+    ds2.close()
+
+
+def test_write_netcdf_fill_value(tmp_path):
+    # Test that NaN values are written with correct fill value
+    arr = np.array([1.0, np.nan, 3.0], dtype=np.float32)
+    ds = xr.Dataset({'bar': (('x',), arr)})
+    out_file = tmp_path / 'test_fill.nc'
+    write_netcdf(ds, str(out_file))
+    ds2 = xr.open_dataset(out_file)
+    # The second value should be the default fill value for float32
+    fill_value = ds2['bar'].encoding.get('_FillValue', None)
+    assert fill_value is not None
+    assert np.isnan(ds2['bar'].values[1])
+    ds2.close()
+
+
+def test_write_netcdf_string_dim_name(tmp_path):
+    # Test that custom char_dim_name is used in encoding
+    arr = np.array([b'abc', b'def'])
+    ds = xr.Dataset({'baz': (('x',), arr)})
+    out_file = tmp_path / 'test_strdim.nc'
+    write_netcdf(ds, str(out_file), char_dim_name='CustomStrLen')
+    ds2 = xr.open_dataset(out_file)
+    # Should have the variable and correct shape
+    assert 'baz' in ds2.variables
+    ds2.close()
+    arr = np.array([1, 2, 3], dtype=np.int64)
+    ds = xr.Dataset({'foo': (('x',), arr)})
+    ds['foo'].attrs['myattr'] = 'testattr'
+    out_file = tmp_path / 'test_int64.nc'
+    write_netcdf(ds, str(out_file))
+    ds2 = xr.open_dataset(out_file)
+    # Should be int32, not int64
+    assert ds2['foo'].dtype == np.int32
+    # Attribute should be preserved
+    assert ds2['foo'].attrs['myattr'] == 'testattr'
+    ds2.close()