Merge remote-tracking branch 'upstream/main' into cow-dataframe-const…

…ructor-from-series

doc/source/whatsnew/v2.0.0.rst

@@ -136,9 +136,17 @@ Copy-on-Write improvements
   Series with the default of ``copy=False`` (:issue:`50471`)
 
 - The :class:`DataFrame` constructor, when constructing a DataFrame from a dictionary
-  of Series objects and specifying ``copy=False``, will now use_inf_as_null a lazy copy
+  of Series objects and specifying ``copy=False``, will now use a lazy copy
   of those Series objects for the columns of the DataFrame (:issue:`50777`)
 
+- Trying to set values using chained assignment (for example, ``df["a"][1:3] = 0``)
+  will now always raise an exception when Copy-on-Write is enabled. In this mode,
+  chained assignment can never work because we are always setting into a temporary
+  object that is the result of an indexing operation (getitem), which under
+  Copy-on-Write always behaves as a copy. Thus, assigning through a chain
+  can never update the original Series or DataFrame. Therefore, an informative
+  error is raised to the user instead of silently doing nothing (:issue:`49467`)
+
 Copy-on-Write can be enabled through
 
 .. code-block:: python