Move chained assignment detection to cython for Python 3.14 compat

pandas/_libs/internals.pyx

@@ -1,6 +1,9 @@
 from collections import defaultdict
+import sys
+import warnings
 
 cimport cython
+from cpython cimport PY_VERSION_HEX
 from cpython.object cimport PyObject
 from cpython.pyport cimport PY_SSIZE_T_MAX
 from cpython.slice cimport PySlice_GetIndicesEx
@@ -20,6 +23,9 @@ from numpy cimport (
 cnp.import_array()
 
 from pandas._libs.algos import ensure_int64
+from pandas.errors import ChainedAssignmentError
+from pandas.errors.cow import _chained_assignment_msg
+
 
 from pandas._libs.util cimport (
     is_array,
@@ -996,3 +1002,41 @@ cdef class BlockValuesRefs:
                 return self._has_reference_maybe_locked()
         ELSE:
             return self._has_reference_maybe_locked()
+
+
+cdef extern from "Python.h":
+    """
+    #if PY_VERSION_HEX < 0x030E0000
+    int __Pyx_PyUnstable_Object_IsUniqueReferencedTemporary(PyObject *ref);
+    #else
+    #define __Pyx_PyUnstable_Object_IsUniqueReferencedTemporary \
+        PyUnstable_Object_IsUniqueReferencedTemporary
+    #endif
+    """
+    int PyUnstable_Object_IsUniqueReferencedTemporary\
+        "__Pyx_PyUnstable_Object_IsUniqueReferencedTemporary"(object o) except -1
+
+
+# Python version compatibility for PyUnstable_Object_IsUniqueReferencedTemporary
+cdef inline bint _is_unique_referenced_temporary(object obj) except -1:
+    if PY_VERSION_HEX >= 0x030E0000:
+        # Python 3.14+ has PyUnstable_Object_IsUniqueReferencedTemporary
+        return PyUnstable_Object_IsUniqueReferencedTemporary(obj)
+    else:
+        # Fallback for older Python versions using sys.getrefcount
+        return sys.getrefcount(obj) <= 1
+
+
+cdef class SetitemMixin:
+    # class used in DataFrame and Series for checking for chained assignment
+
+    def __setitem__(self, key, value) -> None:
+        cdef bint is_unique = _is_unique_referenced_temporary(self)
+        if is_unique:
+            warnings.warn(
+                _chained_assignment_msg, ChainedAssignmentError, stacklevel=1
+            )
+        self._setitem(key, value)
+
+    def __delitem__(self, key) -> None:
+        self._delitem(key)

pandas/compat/pickle_compat.py

@@ -22,6 +22,7 @@
     PeriodArray,
     TimedeltaArray,
 )
+from pandas.core.generic import NDFrame
 from pandas.core.internals import BlockManager
 
 if TYPE_CHECKING:
@@ -90,6 +91,10 @@ def load_reduce(self) -> None:
                 cls = args[0]
                 stack[-1] = NDArrayBacked.__new__(*args)
                 return
+            elif args and issubclass(args[0], NDFrame):
+                cls = args[0]
+                stack[-1] = cls.__new__(cls)
+                return
             raise
 
     dispatch[pickle.REDUCE[0]] = load_reduce  # type: ignore[assignment]

pandas/core/frame.py

@@ -48,6 +48,7 @@
     properties,
 )
 from pandas._libs.hashtable import duplicated
+from pandas._libs.internals import SetitemMixin
 from pandas._libs.lib import is_range_indexer
 from pandas.compat import PYPY
 from pandas.compat._constants import REF_COUNT
@@ -60,7 +61,6 @@
 )
 from pandas.errors.cow import (
     _chained_assignment_method_msg,
-    _chained_assignment_msg,
 )
 from pandas.util._decorators import (
     Appender,
@@ -512,7 +512,7 @@
 
 
 @set_module("pandas")
-class DataFrame(NDFrame, OpsMixin):
+class DataFrame(SetitemMixin, NDFrame, OpsMixin):
     """
     Two-dimensional, size-mutable, potentially heterogeneous tabular data.
 
@@ -661,6 +661,11 @@ class DataFrame(NDFrame, OpsMixin):
     #  and ExtensionArray.  Should NOT be overridden by subclasses.
     __pandas_priority__ = 4000
 
+    # override those to avoid inheriting from SetitemMixin (cython generates
+    # them by default)
+    __reduce__ = object.__reduce__
+    __setstate__ = NDFrame.__setstate__
+
     @property
     def _constructor(self) -> type[DataFrame]:
         return DataFrame
@@ -4213,7 +4218,8 @@ def isetitem(self, loc, value) -> None:
         arraylike, refs = self._sanitize_column(value)
         self._iset_item_mgr(loc, arraylike, inplace=False, refs=refs)
 
-    def __setitem__(self, key, value) -> None:
+    # def __setitem__() is implemented in SetitemMixin and dispatches to this method
+    def _setitem(self, key, value) -> None:
         """
         Set item(s) in DataFrame by key.
 
@@ -4297,12 +4303,6 @@ def __setitem__(self, key, value) -> None:
         z  3  50
         # Values for 'a' and 'b' are completely ignored!
         """
-        if not PYPY:
-            if sys.getrefcount(self) <= 3:
-                warnings.warn(
-                    _chained_assignment_msg, ChainedAssignmentError, stacklevel=2
-                )
-
         key = com.apply_if_callable(key, self)
 
         # see if we can slice the rows

pandas/core/generic.py

@@ -4258,8 +4258,9 @@ def _slice(self, slobj: slice, axis: AxisInt = 0) -> Self:
         result = result.__finalize__(self)
         return result
 
+    # def __delitem__() is implemented in SetitemMixin and dispatches to this method
     @final
-    def __delitem__(self, key) -> None:
+    def _delitem(self, key) -> None:
         """
         Delete item
         """

pandas/core/series.py

@@ -33,6 +33,7 @@
     properties,
     reshape,
 )
+from pandas._libs.internals import SetitemMixin
 from pandas._libs.lib import is_range_indexer
 from pandas.compat import PYPY
 from pandas.compat._constants import REF_COUNT
@@ -45,7 +46,6 @@
 )
 from pandas.errors.cow import (
     _chained_assignment_method_msg,
-    _chained_assignment_msg,
 )
 from pandas.util._decorators import (
     Appender,
@@ -235,7 +235,7 @@
 # class "NDFrame")
 # definition in base class "NDFrame"
 @set_module("pandas")
-class Series(base.IndexOpsMixin, NDFrame):  # type: ignore[misc]
+class Series(SetitemMixin, base.IndexOpsMixin, NDFrame):  # type: ignore[misc]
     """
     One-dimensional ndarray with axis labels (including time series).
 
@@ -363,6 +363,11 @@ class Series(base.IndexOpsMixin, NDFrame):  # type: ignore[misc]
     )
     _mgr: SingleBlockManager
 
+    # override those to avoid inheriting from SetitemMixin (cython generates
+    # them by default)
+    __reduce__ = object.__reduce__
+    __setstate__ = NDFrame.__setstate__
+
     # ----------------------------------------------------------------------
     # Constructors
 
@@ -1059,13 +1064,8 @@ def _get_value(self, label, takeable: bool = False):
         else:
             return self.iloc[loc]
 
-    def __setitem__(self, key, value) -> None:
-        if not PYPY:
-            if sys.getrefcount(self) <= 3:
-                warnings.warn(
-                    _chained_assignment_msg, ChainedAssignmentError, stacklevel=2
-                )
-
+    # def __setitem__() is implemented in SetitemMixin and dispatches to this method
+    def _setitem(self, key, value) -> None:
         check_dict_or_set_indexers(key)
         key = com.apply_if_callable(key, self)
 

pandas/tests/io/test_spss.py

@@ -11,10 +11,6 @@
 pyreadstat = pytest.importorskip("pyreadstat")
 
 
-# TODO(CoW) - detection of chained assignment in cython
-# https://github.com/pandas-dev/pandas/issues/51315
-@pytest.mark.filterwarnings("ignore::pandas.errors.ChainedAssignmentError")
-@pytest.mark.filterwarnings("ignore:ChainedAssignmentError:FutureWarning")
 @pytest.mark.parametrize("path_klass", [lambda p: p, Path])
 def test_spss_labelled_num(path_klass, datapath):
     # test file from the Haven project (https://haven.tidyverse.org/)
@@ -31,8 +27,6 @@ def test_spss_labelled_num(path_klass, datapath):
     tm.assert_frame_equal(df, expected)
 
 
-@pytest.mark.filterwarnings("ignore::pandas.errors.ChainedAssignmentError")
-@pytest.mark.filterwarnings("ignore:ChainedAssignmentError:FutureWarning")
 def test_spss_labelled_num_na(datapath):
     # test file from the Haven project (https://haven.tidyverse.org/)
     # Licence at LICENSES/HAVEN_LICENSE, LICENSES/HAVEN_MIT
@@ -48,8 +42,6 @@ def test_spss_labelled_num_na(datapath):
     tm.assert_frame_equal(df, expected)
 
 
-@pytest.mark.filterwarnings("ignore::pandas.errors.ChainedAssignmentError")
-@pytest.mark.filterwarnings("ignore:ChainedAssignmentError:FutureWarning")
 def test_spss_labelled_str(datapath):
     # test file from the Haven project (https://haven.tidyverse.org/)
     # Licence at LICENSES/HAVEN_LICENSE, LICENSES/HAVEN_MIT
@@ -65,8 +57,6 @@ def test_spss_labelled_str(datapath):
     tm.assert_frame_equal(df, expected)
 
 
-@pytest.mark.filterwarnings("ignore::pandas.errors.ChainedAssignmentError")
-@pytest.mark.filterwarnings("ignore:ChainedAssignmentError:FutureWarning")
 def test_spss_kwargs(datapath):
     # test file from the Haven project (https://haven.tidyverse.org/)
     # Licence at LICENSES/HAVEN_LICENSE, LICENSES/HAVEN_MIT
@@ -81,8 +71,6 @@ def test_spss_kwargs(datapath):
     tm.assert_frame_equal(df, expected)
 
 
-@pytest.mark.filterwarnings("ignore::pandas.errors.ChainedAssignmentError")
-@pytest.mark.filterwarnings("ignore:ChainedAssignmentError:FutureWarning")
 def test_spss_umlauts(datapath):
     # test file from the Haven project (https://haven.tidyverse.org/)
     # Licence at LICENSES/HAVEN_LICENSE, LICENSES/HAVEN_MIT
@@ -140,8 +128,6 @@ def test_invalid_dtype_backend():
         pd.read_spss("test", dtype_backend="numpy")
 
 
-@pytest.mark.filterwarnings("ignore::pandas.errors.ChainedAssignmentError")
-@pytest.mark.filterwarnings("ignore:ChainedAssignmentError:FutureWarning")
 def test_spss_metadata(datapath):
     # GH 54264
     fname = datapath("io", "data", "spss", "labelled-num.sav")