BUG: at/iat __setitem__ failing to cast

doc/source/whatsnew/v1.3.0.rst

@@ -341,6 +341,8 @@ Indexing
 - Bug in incorrectly raising in :meth:`Index.insert`, when setting a new column that cannot be held in the existing ``frame.columns``, or in :meth:`Series.reset_index` or :meth:`DataFrame.reset_index` instead of casting to a compatible dtype (:issue:`39068`)
 - Bug in :meth:`RangeIndex.append` where a single object of length 1 was concatenated incorrectly (:issue:`39401`)
 - Bug in setting ``numpy.timedelta64`` values into an object-dtype :class:`Series` using a boolean indexer (:issue:`39488`)
+- Bug in setting numeric values into a into a boolean-dtypes :class:`Series` using ``at`` or ``iat`` failing to cast to object-dtype (:issue:`39582`)
+-
 
 Missing
 ^^^^^^^

pandas/core/series.py

@@ -1043,17 +1043,17 @@ def _set_value(self, label, value, takeable: bool = False):
             Scalar value.
         takeable : interpret the index as indexers, default False
         """
-        try:
-            if takeable:
-                self._values[label] = value
-            else:
+        if not takeable:
+            try:
                 loc = self.index.get_loc(label)
-                validate_numeric_casting(self.dtype, value)
-                self._values[loc] = value
-        except KeyError:
+            except KeyError:
+                # set using a non-recursive method
+                self.loc[label] = value
+                return
+        else:
+            loc = label
 
-            # set using a non-recursive method
-            self.loc[label] = value
+        self._set_values(loc, value)
 
     # ----------------------------------------------------------------------
     # Unsorted

pandas/tests/series/indexing/test_setitem.py

@@ -326,6 +326,11 @@ def test_int_key(self, obj, key, expected, val, indexer_sli):
 
         self.check_indexer(obj, key, expected, val, indexer_sli)
 
+        if indexer_sli is tm.loc:
+            self.check_indexer(obj, key, expected, val, tm.at)
+        elif indexer_sli is tm.iloc:
+            self.check_indexer(obj, key, expected, val, tm.iat)
+
         rng = range(key, key + 1)
         self.check_indexer(obj, rng, expected, val, indexer_sli)