From c9f998c2b3fa677e325344d0d1737cc6be60a768 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <patrick_hoefler@gmx.net>
Date: Thu, 29 Dec 2022 22:04:28 +0100
Subject: [PATCH 1/2] ENH: Add lazy copy for sort_index

---
 pandas/conftest.py                     |  1 +
 pandas/core/generic.py                 |  2 +-
 pandas/tests/copy_view/test_methods.py | 17 +++++++++++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/pandas/conftest.py b/pandas/conftest.py
index 3b167d9ef4fe2..14c4e59778c9a 100644
--- a/pandas/conftest.py
+++ b/pandas/conftest.py
@@ -1903,6 +1903,7 @@ def using_copy_on_write() -> bool:
     """
     Fixture to check if Copy-on-Write is enabled.
     """
+    pd.options.mode.copy_on_write = True
     return pd.options.mode.copy_on_write and pd.options.mode.data_manager == "block"
 
 
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index c893e9ce3d9a9..23eb66abb8561 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -4934,7 +4934,7 @@ def sort_index(
             if inplace:
                 result = self
             else:
-                result = self.copy()
+                result = self.copy(deep=None)
 
             if ignore_index:
                 result.index = default_index(len(self))
diff --git a/pandas/tests/copy_view/test_methods.py b/pandas/tests/copy_view/test_methods.py
index 878f1d8089d33..dc0bf01c84c74 100644
--- a/pandas/tests/copy_view/test_methods.py
+++ b/pandas/tests/copy_view/test_methods.py
@@ -405,6 +405,23 @@ def test_reindex_like(using_copy_on_write):
     tm.assert_frame_equal(df, df_orig)
 
 
+def test_sort_index(using_copy_on_write):
+    # GH 49473
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+    ser2 = ser.sort_index()
+
+    if using_copy_on_write:
+        assert np.shares_memory(ser.values, ser2.values)
+    else:
+        assert not np.shares_memory(ser.values, ser2.values)
+
+    # mutating ser triggers a copy-on-write for the column / block
+    ser2.iloc[0] = 0
+    assert not np.shares_memory(ser2.values, ser.values)
+    tm.assert_series_equal(ser, ser_orig)
+
+
 def test_reorder_levels(using_copy_on_write):
     index = MultiIndex.from_tuples(
         [(1, 1), (1, 2), (2, 1), (2, 2)], names=["one", "two"]

From 0a5c9e675930d552ad9e66584a865060fb332062 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Tue, 3 Jan 2023 09:57:12 +0100
Subject: [PATCH 2/2] Update conftest.py

---
 pandas/conftest.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pandas/conftest.py b/pandas/conftest.py
index 14c4e59778c9a..3b167d9ef4fe2 100644
--- a/pandas/conftest.py
+++ b/pandas/conftest.py
@@ -1903,7 +1903,6 @@ def using_copy_on_write() -> bool:
     """
     Fixture to check if Copy-on-Write is enabled.
     """
-    pd.options.mode.copy_on_write = True
     return pd.options.mode.copy_on_write and pd.options.mode.data_manager == "block"