Consistently use BytesIOProxy

Author: shoyer

xarray/backends/api.py

@@ -2124,7 +2124,7 @@ def to_netcdf(
 
     if path_or_file is None:
         assert isinstance(target, BytesIOProxy)  # created in this function
-        return target.getvalue_or_getbuffer()
+        return target.getbuffer()
 
     if not compute:
         return delayed_close_after_writes(writes, store)

xarray/backends/common.py

@@ -11,7 +11,6 @@
     TYPE_CHECKING,
     Any,
     ClassVar,
-    Generic,
     Self,
     TypeVar,
     Union,
@@ -198,18 +197,13 @@ def _normalize_path_list(
     return _normalize_path_list(paths)
 
 
-BytesOrMemory = TypeVar("BytesOrMemory", bytes, memoryview)
-
-
 @dataclass
-class BytesIOProxy(Generic[BytesOrMemory]):
-    """Proxy object for a write that returns either bytes or a memoryview."""
+class BytesIOProxy:
+    """Proxy object for a write that a memoryview."""
 
-    # TODO: remove this in favor of BytesIO when Dataset.to_netcdf() stops
-    # returning bytes from the scipy engine
-    getvalue: Callable[[], BytesOrMemory] | None = None
+    getvalue: Callable[[], memoryview] | None = None
 
-    def getvalue_or_getbuffer(self) -> BytesOrMemory:
+    def getbuffer(self) -> memoryview:
         """Get the value of this write as bytes or memory."""
         if self.getvalue is None:
             raise ValueError("must set getvalue before fetching value")

xarray/core/datatree_io.py

@@ -13,7 +13,7 @@
     get_writable_netcdf_store,
     get_writable_zarr_store,
 )
-from xarray.backends.common import ArrayWriter
+from xarray.backends.common import ArrayWriter, BytesIOProxy
 from xarray.backends.locks import get_dask_scheduler
 from xarray.core.datatree import DataTree
 from xarray.core.types import NetcdfWriteModes, ZarrWriteModes
@@ -81,11 +81,9 @@ def _datatree_to_netcdf(
         if not compute:
             raise NotImplementedError(
                 "to_netcdf() with compute=False is not yet implemented when "
-                "returning bytes"
+                "returning a memoryview"
             )
-        # No need to use BytesIOProxy here because the legacy scipy backend
-        # cannot write netCDF files with groups
-        target = io.BytesIO()
+        target = BytesIOProxy()
     else:
         target = filepath  # type: ignore[assignment]
 
@@ -139,7 +137,7 @@ def _datatree_to_netcdf(
             root_store.sync()
 
     if filepath is None:
-        assert isinstance(target, io.BytesIO)
+        assert isinstance(target, BytesIOProxy)  # created in this function
         return target.getbuffer()
 
     if not compute: