Backport PR #44195: Fix series with none equals float series (#44229)

Co-authored-by: Tobias Pitters <[email protected]>

Author: meeseeksmachine

doc/source/whatsnew/v1.3.5.rst

@@ -14,6 +14,7 @@ including other versions of pandas.
 
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
+- Fixed regression in :meth:`Series.equals` when comparing floats with dtype object to None (:issue:`44190`)
 - Fixed performance regression in :func:`read_csv` (:issue:`44106`)
 -
 

pandas/_libs/missing.pyx

@@ -64,7 +64,7 @@ cpdef bint is_matching_na(object left, object right, bint nan_matches_none=False
     elif left is NaT:
         return right is NaT
     elif util.is_float_object(left):
-        if nan_matches_none and right is None:
+        if nan_matches_none and right is None and util.is_nan(left):
             return True
         return (
             util.is_nan(left)

pandas/tests/series/methods/test_equals.py

@@ -125,3 +125,18 @@ def test_equals_none_vs_nan():
     assert ser.equals(ser2)
     assert Index(ser).equals(Index(ser2))
     assert ser.array.equals(ser2.array)
+
+
+def test_equals_None_vs_float():
+    # GH#44190
+    left = Series([-np.inf, np.nan, -1.0, 0.0, 1.0, 10 / 3, np.inf], dtype=object)
+    right = Series([None] * len(left))
+
+    # these series were found to be equal due to a bug, check that they are correctly
+    # found to not equal
+    assert not left.equals(right)
+    assert not right.equals(left)
+    assert not left.to_frame().equals(right.to_frame())
+    assert not right.to_frame().equals(left.to_frame())
+    assert not Index(left, dtype="object").equals(Index(right, dtype="object"))
+    assert not Index(right, dtype="object").equals(Index(left, dtype="object"))