DEPR: automatic alignment on frame.__cmp__(series) (#36795)

Author: jbrockmendel

doc/source/whatsnew/v1.2.0.rst

@@ -266,6 +266,7 @@ Deprecations
 - Deprecated indexing :class:`DataFrame` rows with datetime-like strings ``df[string]``, use ``df.loc[string]`` instead (:issue:`36179`)
 - Deprecated casting an object-dtype index of ``datetime`` objects to :class:`DatetimeIndex` in the :class:`Series` constructor (:issue:`23598`)
 - Deprecated :meth:`Index.is_all_dates` (:issue:`27744`)
+- Deprecated automatic alignment on comparison operations between :class:`DataFrame` and :class:`Series`, do ``frame, ser = frame.align(ser, axis=1, copy=False)`` before e.g. ``frame == ser`` (:issue:`28759`)
 - :meth:`Rolling.count` with ``min_periods=None`` will default to the size of the window in a future version (:issue:`31302`)
 
 .. ---------------------------------------------------------------------------

pandas/core/ops/__init__.py

@@ -5,6 +5,7 @@
 """
 import operator
 from typing import TYPE_CHECKING, Optional, Set, Type
+import warnings
 
 import numpy as np
 
@@ -488,6 +489,18 @@ def to_series(right):
  elif isinstance(right, ABCSeries):
  # axis=1 is default for DataFrame-with-Series op
  axis = left._get_axis_number(axis) if axis is not None else 1
+
+ if not flex:
+ if not left.axes[axis].equals(right.index):
+ warnings.warn(
+ "Automatic reindexing on DataFrame vs Series comparisons "
+ "is deprecated and will raise ValueError in a future version. "
+ "Do `left, right = left.align(right, axis=1, copy=False)` "
+ "before e.g. `left == right`",
+ FutureWarning,
+ stacklevel=3,
+ )
+
  left, right = left.align(
  right, join="outer", axis=axis, level=level, copy=False
  )

pandas/tests/arithmetic/test_datetime64.py

@@ -318,23 +318,32 @@ def test_dt64arr_timestamp_equality(self, box_with_array):
  expected = tm.box_expected([False, True], xbox)
  tm.assert_equal(result, expected)
 
- result = ser != ser[0]
+ warn = FutureWarning if box_with_array is pd.DataFrame else None
+ with tm.assert_produces_warning(warn):
+ # alignment for frame vs series comparisons deprecated
+ result = ser != ser[0]
  expected = tm.box_expected([False, True], xbox)
  tm.assert_equal(result, expected)
 
- result = ser != ser[1]
+ with tm.assert_produces_warning(warn):
+ # alignment for frame vs series comparisons deprecated
+ result = ser != ser[1]
  expected = tm.box_expected([True, True], xbox)
  tm.assert_equal(result, expected)
 
  result = ser == ser
  expected = tm.box_expected([True, False], xbox)
  tm.assert_equal(result, expected)
 
- result = ser == ser[0]
+ with tm.assert_produces_warning(warn):
+ # alignment for frame vs series comparisons deprecated
+ result = ser == ser[0]
  expected = tm.box_expected([True, False], xbox)
  tm.assert_equal(result, expected)
 
- result = ser == ser[1]
+ with tm.assert_produces_warning(warn):
+ # alignment for frame vs series comparisons deprecated
+ result = ser == ser[1]
  expected = tm.box_expected([False, False], xbox)
  tm.assert_equal(result, expected)
 

pandas/tests/frame/test_arithmetic.py

@@ -795,13 +795,17 @@ def test_frame_with_zero_len_series_corner_cases():
  expected = pd.DataFrame(df.values * np.nan, columns=df.columns)
  tm.assert_frame_equal(result, expected)
 
- result = df == ser
+ with tm.assert_produces_warning(FutureWarning):
+ # Automatic alignment for comparisons deprecated
+ result = df == ser
  expected = pd.DataFrame(False, index=df.index, columns=df.columns)
  tm.assert_frame_equal(result, expected)
 
  # non-float case should not raise on comparison
  df2 = pd.DataFrame(df.values.view("M8[ns]"), columns=df.columns)
- result = df2 == ser
+ with tm.assert_produces_warning(FutureWarning):
+ # Automatic alignment for comparisons deprecated
+ result = df2 == ser
  expected = pd.DataFrame(False, index=df.index, columns=df.columns)
  tm.assert_frame_equal(result, expected)