Merge remote-tracking branch 'upstream/main' into cow-constructor-fro…

…m-pandas

doc/source/whatsnew/v2.0.0.rst

@@ -83,13 +83,57 @@ be set to ``"pyarrow"`` to return pyarrow-backed, nullable :class:`ArrowDtype` (
         df_pyarrow = pd.read_csv(data, use_nullable_dtypes=True, engine="pyarrow")
     df_pyarrow.dtypes
 
-Copy on write improvements
+Copy-on-Write improvements
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-* The :class:`Series` constructor will now create a lazy copy (deferring the copy until
+- A new lazy copy mechanism that defers the copy until the object in question is modified
+  was added to the following methods:
+
+  - :meth:`DataFrame.reset_index` / :meth:`Series.reset_index`
+  - :meth:`DataFrame.set_index` / :meth:`Series.set_index`
+  - :meth:`DataFrame.set_axis` / :meth:`Series.set_axis`
+  - :meth:`DataFrame.rename_axis` / :meth:`Series.rename_axis`
+  - :meth:`DataFrame.rename_columns`
+  - :meth:`DataFrame.reindex` / :meth:`Series.reindex`
+  - :meth:`DataFrame.reindex_like` / :meth:`Series.reindex_like`
+  - :meth:`DataFrame.assign`
+  - :meth:`DataFrame.drop`
+  - :meth:`DataFrame.dropna` / :meth:`Series.dropna`
+  - :meth:`DataFrame.select_dtypes`
+  - :meth:`DataFrame.align` / :meth:`Series.align`
+  - :meth:`Series.to_frame`
+  - :meth:`DataFrame.rename` / :meth:`Series.rename`
+  - :meth:`DataFrame.add_prefix` / :meth:`Series.add_prefix`
+  - :meth:`DataFrame.add_suffix` / :meth:`Series.add_suffix`
+  - :meth:`DataFrame.drop_duplicates` / :meth:`Series.drop_duplicates`
+  - :meth:`DataFrame.reorder_levels` / :meth:`Series.reorder_levels`
+
+  These methods return views when Copy-on-Write is enabled, which provides a significant
+  performance improvement compared to the regular execution (:issue:`49473`).
+
+- Accessing a single column of a DataFrame as a Series (e.g. ``df["col"]``) now always
+  returns a new object every time it is constructed when Copy-on-Write is enabled (not
+  returning multiple times an identical, cached Series object). This ensures that those
+  Series objects correctly follow the Copy-on-Write rules (:issue:`49450`)
+
+- The :class:`Series` constructor will now create a lazy copy (deferring the copy until
   a modification to the data happens) when constructing a Series from an existing
   Series with the default of ``copy=False`` (:issue:`50471`)
 
+Copy-on-Write can be enabled through
+
+.. code-block:: python
+
+    pd.set_option("mode.copy_on_write", True)
+    pd.options.mode.copy_on_write = True
+
+Alternatively, copy on write can be enabled locally through:
+
+.. code-block:: python
+
+    with pd.option_context("mode.copy_on_write", True):
+        ...
+
 .. _whatsnew_200.enhancements.other:
 
 Other enhancements