From ca9eb22763ac246227a815afc9401588138968b3 Mon Sep 17 00:00:00 2001
From: Tobias Pitters <31857876+closechoice@users.noreply.github.com>
Date: Fri, 19 Aug 2022 12:21:24 +0200
Subject: [PATCH 1/2] REGR: fix eval with inplace=True to correctly update
 column values inplace (#47550)

* fix pre-commit issues

* fix linting errors

* add inplace argument to isetitem and use in eval

* changes due to PR discussions

* fix issues

* update eval

* update whatsnew

* add PR suggestions

* update imports in eval.py

* check inplace and use NDFrame + small update to test

* update test to use using_copy_on_write

* skip test for array manager

Co-authored-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>
---
 doc/source/whatsnew/v1.4.4.rst        |  1 +
 pandas/core/computation/eval.py       |  6 +++++-
 pandas/tests/computation/test_eval.py | 20 ++++++++++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v1.4.4.rst b/doc/source/whatsnew/v1.4.4.rst
index 57b8fdee5888a..1e7ed256c05ef 100644
--- a/doc/source/whatsnew/v1.4.4.rst
+++ b/doc/source/whatsnew/v1.4.4.rst
@@ -19,6 +19,7 @@ Fixed regressions
 - Fixed regression in :meth:`DataFrame.loc` not updating the cache correctly after values were set (:issue:`47867`)
 - Fixed regression in :meth:`DataFrame.loc` not aligning index in some cases when setting a :class:`DataFrame` (:issue:`47578`)
 - Fixed regression in setting ``None`` or non-string value into a ``string``-dtype Series using a mask (:issue:`47628`)
+- Fixed regression in :meth:`DataFrame.eval` creating a copy when updating inplace (:issue:`47449`)
 -
 
 .. ---------------------------------------------------------------------------
diff --git a/pandas/core/computation/eval.py b/pandas/core/computation/eval.py
index d82cc37b90ad4..70a8bff5d509c 100644
--- a/pandas/core/computation/eval.py
+++ b/pandas/core/computation/eval.py
@@ -18,6 +18,7 @@
 from pandas.core.computation.ops import BinOp
 from pandas.core.computation.parsing import tokenize_string
 from pandas.core.computation.scope import ensure_scope
+from pandas.core.generic import NDFrame
 
 from pandas.io.formats.printing import pprint_thing
 
@@ -384,7 +385,10 @@ def eval(
             try:
                 with warnings.catch_warnings(record=True):
                     # TODO: Filter the warnings we actually care about here.
-                    target[assigner] = ret
+                    if inplace and isinstance(target, NDFrame):
+                        target.loc[:, assigner] = ret
+                    else:
+                        target[assigner] = ret
             except (TypeError, IndexError) as err:
                 raise ValueError("Cannot assign expression output to target") from err
 
diff --git a/pandas/tests/computation/test_eval.py b/pandas/tests/computation/test_eval.py
index 3517068b3d0cc..2dad8132dced7 100644
--- a/pandas/tests/computation/test_eval.py
+++ b/pandas/tests/computation/test_eval.py
@@ -1966,6 +1966,26 @@ def test_negate_lt_eq_le(engine, parser):
         tm.assert_frame_equal(result, expected)
 
 
+@td.skip_array_manager_not_yet_implemented
+def test_set_inplace(using_copy_on_write):
+    # https://github.com/pandas-dev/pandas/issues/47449
+    # Ensure we don't only update the DataFrame inplace, but also the actual
+    # column values, such that references to this column also get updated
+    df = DataFrame({"A": [1, 2, 3], "B": [4, 5, 6], "C": [7, 8, 9]})
+    result_view = df[:]
+    ser = df["A"]
+    df.eval("A = B + C", inplace=True)
+    expected = DataFrame({"A": [11, 13, 15], "B": [4, 5, 6], "C": [7, 8, 9]})
+    tm.assert_frame_equal(df, expected)
+    if not using_copy_on_write:
+        tm.assert_series_equal(ser, expected["A"])
+        tm.assert_series_equal(result_view["A"], expected["A"])
+    else:
+        expected = Series([1, 2, 3], name="A")
+        tm.assert_series_equal(ser, expected)
+        tm.assert_series_equal(result_view["A"], expected)
+
+
 class TestValidate:
     @pytest.mark.parametrize("value", [1, "True", [1, 2, 3], 5.0])
     def test_validate_bool_args(self, value):

From 9aed9c7fc569fbd6db29fb560fbbebaa19f2c485 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <patrick_hoefler@gmx.net>
Date: Fri, 19 Aug 2022 14:07:31 +0200
Subject: [PATCH 2/2] Remove copy on write fixture

---
 pandas/tests/computation/test_eval.py | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/pandas/tests/computation/test_eval.py b/pandas/tests/computation/test_eval.py
index 2dad8132dced7..3051683853a46 100644
--- a/pandas/tests/computation/test_eval.py
+++ b/pandas/tests/computation/test_eval.py
@@ -1967,7 +1967,7 @@ def test_negate_lt_eq_le(engine, parser):
 
 
 @td.skip_array_manager_not_yet_implemented
-def test_set_inplace(using_copy_on_write):
+def test_set_inplace():
     # https://github.com/pandas-dev/pandas/issues/47449
     # Ensure we don't only update the DataFrame inplace, but also the actual
     # column values, such that references to this column also get updated
@@ -1977,13 +1977,8 @@ def test_set_inplace(using_copy_on_write):
     df.eval("A = B + C", inplace=True)
     expected = DataFrame({"A": [11, 13, 15], "B": [4, 5, 6], "C": [7, 8, 9]})
     tm.assert_frame_equal(df, expected)
-    if not using_copy_on_write:
-        tm.assert_series_equal(ser, expected["A"])
-        tm.assert_series_equal(result_view["A"], expected["A"])
-    else:
-        expected = Series([1, 2, 3], name="A")
-        tm.assert_series_equal(ser, expected)
-        tm.assert_series_equal(result_view["A"], expected)
+    tm.assert_series_equal(ser, expected["A"])
+    tm.assert_series_equal(result_view["A"], expected["A"])
 
 
 class TestValidate: