CoW: Add warning for interpolate with inplace (#56066)

Author: phofl

pandas/core/generic.py

@@ -7462,6 +7462,18 @@ def ffill(
  ChainedAssignmentError,
  stacklevel=2,
  )
+ elif not PYPY and not using_copy_on_write():
+ ctr = sys.getrefcount(self)
+ ref_count = REF_COUNT
+ if isinstance(self, ABCSeries) and hasattr(self, "_cacher"):
+ # see https://github.com/pandas-dev/pandas/pull/56060#discussion_r1399245221
+ ref_count += 1
+ if ctr <= ref_count:
+ warnings.warn(
+ _chained_assignment_warning_method_msg,
+ FutureWarning,
+ stacklevel=2,
+ )
 
  return self._pad_or_backfill(
  "ffill",
@@ -7633,6 +7645,19 @@ def bfill(
  ChainedAssignmentError,
  stacklevel=2,
  )
+ elif not PYPY and not using_copy_on_write():
+ ctr = sys.getrefcount(self)
+ ref_count = REF_COUNT
+ if isinstance(self, ABCSeries) and hasattr(self, "_cacher"):
+ # see https://github.com/pandas-dev/pandas/pull/56060#discussion_r1399245221
+ ref_count += 1
+ if ctr <= ref_count:
+ warnings.warn(
+ _chained_assignment_warning_method_msg,
+ FutureWarning,
+ stacklevel=2,
+ )
+
  return self._pad_or_backfill(
  "bfill",
  axis=axis,
@@ -8227,6 +8252,18 @@ def interpolate(
  ChainedAssignmentError,
  stacklevel=2,
  )
+ elif not PYPY and not using_copy_on_write():
+ ctr = sys.getrefcount(self)
+ ref_count = REF_COUNT
+ if isinstance(self, ABCSeries) and hasattr(self, "_cacher"):
+ # see https://github.com/pandas-dev/pandas/pull/56060#discussion_r1399245221
+ ref_count += 1
+ if ctr <= ref_count:
+ warnings.warn(
+ _chained_assignment_warning_method_msg,
+ FutureWarning,
+ stacklevel=2,
+ )
 
  axis = self._get_axis_number(axis)
 

pandas/tests/copy_view/test_interp_fillna.py

@@ -390,3 +390,14 @@ def test_interpolate_chained_assignment(using_copy_on_write, func):
  with tm.raises_chained_assignment_error():
  getattr(df[["a"]], func)(inplace=True)
  tm.assert_frame_equal(df, df_orig)
+ else:
+ 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 option_context("mode.chained_assignment", None):
+ getattr(df[["a"]], func)(inplace=True)
+
+ with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+ with option_context("mode.chained_assignment", None):
+ getattr(df[df["a"] > 1], func)(inplace=True)

pandas/tests/frame/methods/test_interpolate.py

@@ -378,7 +378,8 @@ def test_interp_inplace(self, using_copy_on_write):
  assert return_value is None
  tm.assert_frame_equal(result, expected_cow)
  else:
- return_value = result["a"].interpolate(inplace=True)
+ with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+ return_value = result["a"].interpolate(inplace=True)
  assert return_value is None
  tm.assert_frame_equal(result, expected)