use lib.is_integer + add test covering it

Author: jorisvandenbossche

pandas/core/internals/managers.py

@@ -575,7 +575,7 @@ def setitem(self, indexer, value) -> Self:
 
                     indexer = list(indexer)
                     # first block equals values we are setting to -> set to all columns
-                    if isinstance(indexer[1], int):
+                    if lib.is_integer(indexer[1]):
                         col_indexer = 0
                     elif len(blk_loc) > 1:
                         col_indexer = slice(None)  # type: ignore[assignment]

pandas/tests/frame/indexing/test_setitem.py

@@ -1409,6 +1409,9 @@ def test_iloc_setitem_view_2dblock(self):
             ((slice(None), slice(None)), 2),
             ((0, [1, 3]), [2, 2]),
             (([0], 1), [2]),
+            (([0], np.int64(1)), [2]),
+            ((slice(None), np.int64(1)), [2, 2, 2]),
+            ((slice(None, 2), np.int64(1)), [2, 2]),
             (
                 (np.array([False, True, False]), np.array([False, True, False, True])),
                 [2, 2],