From 627df2272a848e12da2c3f2dd0d4e1e6063c2b4d Mon Sep 17 00:00:00 2001
From: Illviljan <14371165+Illviljan@users.noreply.github.com>
Date: Tue, 4 Jun 2024 21:27:59 +0200
Subject: [PATCH 1/2] Add typing

---
 xarray/backends/api.py | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/xarray/backends/api.py b/xarray/backends/api.py
index 76fcac62cd3..561cd7abc2a 100644
--- a/xarray/backends/api.py
+++ b/xarray/backends/api.py
@@ -55,6 +55,7 @@
         JoinOptions,
         NestedSequence,
         T_Chunks,
+        T_Dataset,
     )
 
     T_NetcdfEngine = Literal["netcdf4", "scipy", "h5netcdf"]
@@ -231,14 +232,15 @@ def _get_mtime(filename_or_obj):
     return mtime
 
 
-def _protect_dataset_variables_inplace(dataset, cache):
+def _protect_dataset_variables_inplace(dataset: T_Dataset, cache: bool) -> None:
     for name, variable in dataset.variables.items():
         if name not in dataset._indexes:
             # no need to protect IndexVariable objects
             data = indexing.CopyOnWriteArray(variable._data)
             if cache:
-                data = indexing.MemoryCachedArray(data)
-            variable.data = data
+                variable.data = indexing.MemoryCachedArray(data)
+            else:
+                variable.data = data
 
 
 def _finalize_store(write, store):
@@ -305,7 +307,7 @@ def load_dataarray(filename_or_obj, **kwargs):
 
 
 def _chunk_ds(
-    backend_ds,
+    backend_ds: T_Dataset,
     filename_or_obj,
     engine,
     chunks,
@@ -314,7 +316,7 @@ def _chunk_ds(
     chunked_array_type,
     from_array_kwargs,
     **extra_tokens,
-):
+) -> T_Dataset:
     chunkmanager = guess_chunkmanager(chunked_array_type)
 
     # TODO refactor to move this dask-specific logic inside the DaskManager class
@@ -322,7 +324,7 @@ def _chunk_ds(
         from dask.base import tokenize
 
         mtime = _get_mtime(filename_or_obj)
-        token = tokenize(filename_or_obj, mtime, engine, chunks, **extra_tokens)
+        token: Any = tokenize(filename_or_obj, mtime, engine, chunks, **extra_tokens)
         name_prefix = "open_dataset-"
     else:
         # not used
@@ -347,7 +349,7 @@ def _chunk_ds(
 
 
 def _dataset_from_backend_dataset(
-    backend_ds,
+    backend_ds: T_Dataset,
     filename_or_obj,
     engine,
     chunks,
@@ -357,7 +359,7 @@ def _dataset_from_backend_dataset(
     chunked_array_type,
     from_array_kwargs,
     **extra_tokens,
-):
+) -> T_Dataset:
     if not isinstance(chunks, (int, dict)) and chunks not in {None, "auto"}:
         raise ValueError(
             f"chunks must be an int, dict, 'auto', or None. Instead found {chunks}."

From 44199793952a946aeb410996ca043508471b7e38 Mon Sep 17 00:00:00 2001
From: Illviljan <14371165+Illviljan@users.noreply.github.com>
Date: Tue, 4 Jun 2024 21:32:51 +0200
Subject: [PATCH 2/2] data is already a valid duckarray, no need to recheck

---
 xarray/backends/api.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xarray/backends/api.py b/xarray/backends/api.py
index 561cd7abc2a..a0b9b4ecd18 100644
--- a/xarray/backends/api.py
+++ b/xarray/backends/api.py
@@ -238,9 +238,9 @@ def _protect_dataset_variables_inplace(dataset: T_Dataset, cache: bool) -> None:
             # no need to protect IndexVariable objects
             data = indexing.CopyOnWriteArray(variable._data)
             if cache:
-                variable.data = indexing.MemoryCachedArray(data)
+                variable._data = indexing.MemoryCachedArray(data)
             else:
-                variable.data = data
+                variable._data = data
 
 
 def _finalize_store(write, store):