Fix a regression with scalar indexing due to #1800

docs/release.rst

@@ -31,6 +31,8 @@ Docs
 
 Maintenance
 ~~~~~~~~~~~
+* Fix a regression when getting or setting a single value from arrays with size-1 chunks.
+  By :user:`Deepak Cherian <dcherian>` :issue:`1874`
 
 Deprecations
 ~~~~~~~~~~~~

zarr/core.py

@@ -2030,7 +2030,9 @@ def _process_chunk(
             and not self._filters
             and self._dtype != object
         ):
-            dest = out[out_selection]
+            # For 0D arrays out_selection = () and out[out_selection] is a scalar
+            # Avoid that
+            dest = out[out_selection] if out_selection else out
             # Assume that array-like objects that doesn't have a
             # `writeable` flag is writable.
             dest_is_writable = getattr(dest, "writeable", True)
@@ -2281,8 +2283,11 @@ def _process_for_setitem(self, ckey, chunk_selection, value, fields=None):
                 chunk.fill(value)
 
             else:
-                # ensure array is contiguous
-                chunk = value.astype(self._dtype, order=self._order, copy=False)
+                if not isinstance(value, np.ndarray):
+                    chunk = np.asarray(value, dtype=self._dtype, order=self._order)
+                else:
+                    # ensure array is contiguous
+                    chunk = value.astype(self._dtype, order=self._order, copy=False)
 
         else:
             # partially replace the contents of this chunk

zarr/tests/test_core.py

@@ -3157,3 +3157,22 @@ def test_issue_1279(tmpdir):
 
     written_data = ds_reopened[:]
     assert_array_equal(data, written_data)
+
+
+def test_scalar_indexing():
+    store = zarr.KVStore({})
+
+    store["a"] = zarr.create((3,), chunks=(1,), store=store)
+    store["a"][:] = [1, 2, 3]
+
+    assert store["a"][1] == np.array(2.0)
+    assert store["a"][(1,)] == np.array(2.0)
+
+    store["a"][0] = [-1]
+    assert store["a"][0] == np.array(-1)
+
+    store["a"][0] = -2
+    assert store["a"][0] == np.array(-2)
+
+    store["a"][0] = (-3,)
+    assert store["a"][0] == np.array(-3)