CoW: Avoid warning if temporary object is a copy

pandas/core/frame.py

@@ -8903,7 +8903,7 @@ def update(
                     ChainedAssignmentError,
                     stacklevel=2,
                 )
-        elif not PYPY and not using_copy_on_write():
+        elif not PYPY and not using_copy_on_write() and self._is_view_after_cow_rules():
             if sys.getrefcount(self) <= REF_COUNT:
                 warnings.warn(
                     _chained_assignment_warning_method_msg,

pandas/core/generic.py

@@ -668,6 +668,14 @@ def _get_cleaned_column_resolvers(self) -> dict[Hashable, Series]:
     def _info_axis(self) -> Index:
         return getattr(self, self._info_axis_name)
 
+    def _is_view_after_cow_rules(self):
+        # Only to be used in cases of chained assignment checks, this is a
+        # simplified check that assumes that either the whole object is a view
+        # or a copy
+        if len(self._mgr.blocks) == 0:  # type: ignore[union-attr]
+            return False
+        return self._mgr.blocks[0].refs.has_reference()  # type: ignore[union-attr]
+
     @property
     def shape(self) -> tuple[int, ...]:
         """
@@ -7268,7 +7276,11 @@ def fillna(
                         ChainedAssignmentError,
                         stacklevel=2,
                     )
-            elif not PYPY and not using_copy_on_write():
+            elif (
+                not PYPY
+                and not using_copy_on_write()
+                and self._is_view_after_cow_rules()
+            ):
                 ctr = sys.getrefcount(self)
                 ref_count = REF_COUNT
                 if isinstance(self, ABCSeries) and _check_cacher(self):
@@ -7550,7 +7562,11 @@ def ffill(
                         ChainedAssignmentError,
                         stacklevel=2,
                     )
-            elif not PYPY and not using_copy_on_write():
+            elif (
+                not PYPY
+                and not using_copy_on_write()
+                and self._is_view_after_cow_rules()
+            ):
                 ctr = sys.getrefcount(self)
                 ref_count = REF_COUNT
                 if isinstance(self, ABCSeries) and _check_cacher(self):
@@ -7733,7 +7749,11 @@ def bfill(
                         ChainedAssignmentError,
                         stacklevel=2,
                     )
-            elif not PYPY and not using_copy_on_write():
+            elif (
+                not PYPY
+                and not using_copy_on_write()
+                and self._is_view_after_cow_rules()
+            ):
                 ctr = sys.getrefcount(self)
                 ref_count = REF_COUNT
                 if isinstance(self, ABCSeries) and _check_cacher(self):
@@ -7899,7 +7919,11 @@ def replace(
                         ChainedAssignmentError,
                         stacklevel=2,
                     )
-            elif not PYPY and not using_copy_on_write():
+            elif (
+                not PYPY
+                and not using_copy_on_write()
+                and self._is_view_after_cow_rules()
+            ):
                 ctr = sys.getrefcount(self)
                 ref_count = REF_COUNT
                 if isinstance(self, ABCSeries) and _check_cacher(self):
@@ -8340,7 +8364,11 @@ def interpolate(
                         ChainedAssignmentError,
                         stacklevel=2,
                     )
-            elif not PYPY and not using_copy_on_write():
+            elif (
+                not PYPY
+                and not using_copy_on_write()
+                and self._is_view_after_cow_rules()
+            ):
                 ctr = sys.getrefcount(self)
                 ref_count = REF_COUNT
                 if isinstance(self, ABCSeries) and _check_cacher(self):
@@ -8978,7 +9006,11 @@ def clip(
                         ChainedAssignmentError,
                         stacklevel=2,
                     )
-            elif not PYPY and not using_copy_on_write():
+            elif (
+                not PYPY
+                and not using_copy_on_write()
+                and self._is_view_after_cow_rules()
+            ):
                 ctr = sys.getrefcount(self)
                 ref_count = REF_COUNT
                 if isinstance(self, ABCSeries) and hasattr(self, "_cacher"):
@@ -10926,7 +10958,11 @@ def where(
                         ChainedAssignmentError,
                         stacklevel=2,
                     )
-            elif not PYPY and not using_copy_on_write():
+            elif (
+                not PYPY
+                and not using_copy_on_write()
+                and self._is_view_after_cow_rules()
+            ):
                 ctr = sys.getrefcount(self)
                 ref_count = REF_COUNT
                 if isinstance(self, ABCSeries) and hasattr(self, "_cacher"):
@@ -11005,7 +11041,11 @@ def mask(
                         ChainedAssignmentError,
                         stacklevel=2,
                     )
-            elif not PYPY and not using_copy_on_write():
+            elif (
+                not PYPY
+                and not using_copy_on_write()
+                and self._is_view_after_cow_rules()
+            ):
                 ctr = sys.getrefcount(self)
                 ref_count = REF_COUNT
                 if isinstance(self, ABCSeries) and hasattr(self, "_cacher"):

pandas/core/series.py

@@ -3580,7 +3580,7 @@ def update(self, other: Series | Sequence | Mapping) -> None:
                     ChainedAssignmentError,
                     stacklevel=2,
                 )
-        elif not PYPY and not using_copy_on_write():
+        elif not PYPY and not using_copy_on_write() and self._is_view_after_cow_rules():
             ctr = sys.getrefcount(self)
             ref_count = REF_COUNT
             if _check_cacher(self):

pandas/tests/copy_view/test_clip.py

@@ -92,10 +92,10 @@ def test_clip_chained_inplace(using_copy_on_write):
         with tm.assert_produces_warning(FutureWarning, match="inplace method"):
             df["a"].clip(1, 2, inplace=True)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 df[["a"]].clip(1, 2, inplace=True)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 df[df["a"] > 1].clip(1, 2, inplace=True)

pandas/tests/copy_view/test_interp_fillna.py

@@ -366,11 +366,11 @@ def test_fillna_chained_assignment(using_copy_on_write):
             df[["a"]].fillna(100, inplace=True)
         tm.assert_frame_equal(df, df_orig)
     else:
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 df[["a"]].fillna(100, inplace=True)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 df[df.a > 5].fillna(100, inplace=True)
 
@@ -394,10 +394,10 @@ def test_interpolate_chained_assignment(using_copy_on_write, func):
         with tm.assert_produces_warning(FutureWarning, match="inplace method"):
             getattr(df["a"], func)(inplace=True)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 getattr(df[["a"]], func)(inplace=True)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 getattr(df[df["a"] > 1], func)(inplace=True)

pandas/tests/copy_view/test_methods.py

@@ -1562,11 +1562,11 @@ def test_chained_where_mask(using_copy_on_write, func):
         with tm.assert_produces_warning(FutureWarning, match="inplace method"):
             getattr(df["a"], func)(df["a"] > 2, 5, inplace=True)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 getattr(df[["a"]], func)(df["a"] > 2, 5, inplace=True)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 getattr(df[df["a"] > 1], func)(df["a"] > 2, 5, inplace=True)
 
@@ -1840,11 +1840,11 @@ def test_update_chained_assignment(using_copy_on_write):
         with tm.assert_produces_warning(FutureWarning, match="inplace method"):
             df["a"].update(ser2)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 df[["a"]].update(ser2.to_frame())
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 df[df["a"] > 1].update(ser2.to_frame())
 

pandas/tests/copy_view/test_replace.py

@@ -401,11 +401,11 @@ def test_replace_chained_assignment(using_copy_on_write):
             df[["a"]].replace(1, 100, inplace=True)
         tm.assert_frame_equal(df, df_orig)
     else:
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 df[["a"]].replace(1, 100, inplace=True)
 
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             with option_context("mode.chained_assignment", None):
                 df[df.a > 5].replace(1, 100, inplace=True)
 

pandas/tests/indexing/multiindex/test_chaining_and_caching.py

@@ -34,12 +34,12 @@ def test_detect_chained_assignment(using_copy_on_write, warn_copy_on_write):
         with tm.raises_chained_assignment_error():
             zed["eyes"]["right"].fillna(value=555, inplace=True)
     elif warn_copy_on_write:
-        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+        with tm.assert_produces_warning(None):
             zed["eyes"]["right"].fillna(value=555, inplace=True)
     else:
         msg = "A value is trying to be set on a copy of a slice from a DataFrame"
         with pytest.raises(SettingWithCopyError, match=msg):
-            with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+            with tm.assert_produces_warning(None):
                 zed["eyes"]["right"].fillna(value=555, inplace=True)