FIX: h5py>=3 string decoding (#4893)

* FIX: set `decode_strings=True` for h5netcdf backend, convert object string to byte string if necessary, unpin h5py

* Update strings.py

* Update h5netcdf_.py

* fix style

* FIX:change decode_strings -> decode_vlen_strings, add whats-new.rst entry

* FIX: change missed decode_strings -> decode_vlen_strings

* FIX: set `decode_vlen_strings=True` in `open` classmethod, call remaining tests with `decode_vlen_strings=True`

* FIX: cover tests for h5py=2

ci/requirements/environment-windows.yml

@@ -11,7 +11,7 @@ dependencies:
   - dask
   - distributed
   - h5netcdf
-  - h5py=2
+  - h5py
   - hdf5
   - hypothesis
   - iris

ci/requirements/environment.yml

@@ -13,7 +13,7 @@ dependencies:
   - dask
   - distributed
   - h5netcdf
-  - h5py=2
+  - h5py
   - hdf5
   - hypothesis
   - iris

ci/requirements/py38-all-but-dask.yml

@@ -14,7 +14,7 @@ dependencies:
   - cftime
   - coveralls
   - h5netcdf
-  - h5py=2
+  - h5py
   - hdf5
   - hypothesis
   - lxml    # Optional dep of pydap

doc/whats-new.rst

@@ -118,6 +118,8 @@ Bug fixes
   By `Leif Denby <https://github.com/leifdenby>`_.
 - Fix time encoding bug associated with using cftime versions greater than
   1.4.0 with xarray (:issue:`4870`, :pull:`4871`). By `Spencer Clark <https://github.com/spencerkclark>`_.
+- Fix decoding of vlen strings using h5py versions greater than 3.0.0 with h5netcdf backend (:issue:`4570`, :pull:`4893`).
+  By `Kai Mühlbauer <https://github.com/kmuehlbauer>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/backends/h5netcdf_.py

@@ -131,6 +131,7 @@ def open(
         autoclose=False,
         invalid_netcdf=None,
         phony_dims=None,
+        decode_vlen_strings=True,
     ):
 
         if isinstance(filename, bytes):
@@ -157,6 +158,10 @@ def open(
                     "h5netcdf backend keyword argument 'phony_dims' needs "
                     "h5netcdf >= 0.8.0."
                 )
+        if LooseVersion(h5netcdf.__version__) >= LooseVersion(
+            "0.10.0"
+        ) and LooseVersion(h5netcdf.core.h5py.__version__) >= LooseVersion("3.0.0"):
+            kwargs["decode_vlen_strings"] = decode_vlen_strings
 
         if lock is None:
             if mode == "r":
@@ -358,6 +363,7 @@ def open_dataset(
         lock=None,
         invalid_netcdf=None,
         phony_dims=None,
+        decode_vlen_strings=True,
     ):
 
         store = H5NetCDFStore.open(
@@ -367,6 +373,7 @@ def open_dataset(
             lock=lock,
             invalid_netcdf=invalid_netcdf,
             phony_dims=phony_dims,
+            decode_vlen_strings=decode_vlen_strings,
         )
 
         store_entrypoint = StoreBackendEntrypoint()

xarray/tests/test_backends.py

@@ -2579,13 +2579,19 @@ def test_open_dataset_group(self):
                 v = group.createVariable("x", "int")
                 v[...] = 42
 
-            h5 = h5netcdf.File(tmp_file, mode="r")
+            kwargs = {}
+            if LooseVersion(h5netcdf.__version__) >= LooseVersion(
+                "0.10.0"
+            ) and LooseVersion(h5netcdf.core.h5py.__version__) >= LooseVersion("3.0.0"):
+                kwargs = dict(decode_vlen_strings=True)
+
+            h5 = h5netcdf.File(tmp_file, mode="r", **kwargs)
             store = backends.H5NetCDFStore(h5["g"])
             with open_dataset(store) as ds:
                 expected = Dataset({"x": ((), 42)})
                 assert_identical(expected, ds)
 
-            h5 = h5netcdf.File(tmp_file, mode="r")
+            h5 = h5netcdf.File(tmp_file, mode="r", **kwargs)
             store = backends.H5NetCDFStore(h5, group="g")
             with open_dataset(store) as ds:
                 expected = Dataset({"x": ((), 42)})
@@ -2600,7 +2606,13 @@ def test_deepcopy(self):
                 v = nc.createVariable("y", np.int32, ("x",))
                 v[:] = np.arange(10)
 
-            h5 = h5netcdf.File(tmp_file, mode="r")
+            kwargs = {}
+            if LooseVersion(h5netcdf.__version__) >= LooseVersion(
+                "0.10.0"
+            ) and LooseVersion(h5netcdf.core.h5py.__version__) >= LooseVersion("3.0.0"):
+                kwargs = dict(decode_vlen_strings=True)
+
+            h5 = h5netcdf.File(tmp_file, mode="r", **kwargs)
             store = backends.H5NetCDFStore(h5)
             with open_dataset(store) as ds:
                 copied = ds.copy(deep=True)