disallow np.timedelta64 in is_integer (#27401)

Author: jbrockmendel

pandas/_libs/tslibs/util.pxd

@@ -76,7 +76,8 @@ cdef inline bint is_integer_object(object obj) nogil:
     -----
     This counts np.timedelta64 objects as integers.
     """
-    return not PyBool_Check(obj) and PyArray_IsIntegerScalar(obj)
+    return (not PyBool_Check(obj) and PyArray_IsIntegerScalar(obj)
+            and not is_timedelta64_object(obj))
 
 
 cdef inline bint is_float_object(object obj) nogil:

pandas/core/indexes/timedeltas.py

@@ -593,7 +593,7 @@ def _maybe_cast_slice_bound(self, label, side, kind):
                 return lbound
             else:
                 return lbound + to_offset(parsed.resolution_string) - Timedelta(1, "ns")
-        elif (is_integer(label) or is_float(label)) and not is_timedelta64_dtype(label):
+        elif is_integer(label) or is_float(label):
             self._invalid_indexer("slice", label)
 
         return label

pandas/core/internals/blocks.py

@@ -2609,15 +2609,13 @@ def _can_hold_element(self, element):
             return issubclass(tipo.type, (np.timedelta64, np.int64))
         elif element is NaT:
             return True
-        return is_integer(element) or isinstance(
-            element, (timedelta, np.timedelta64, np.int64)
-        )
+        return is_integer(element) or isinstance(element, (timedelta, np.timedelta64))
 
     def fillna(self, value, **kwargs):
 
         # allow filling with integers to be
         # interpreted as nanoseconds
-        if is_integer(value) and not isinstance(value, np.timedelta64):
+        if is_integer(value):
             # Deprecation GH#24694, GH#19233
             warnings.warn(
                 "Passing integers to fillna is deprecated, will "

pandas/tests/dtypes/test_inference.py

@@ -1203,9 +1203,7 @@ def test_is_integer(self):
         assert not is_integer(Timestamp("2011-01-01", tz="US/Eastern"))
         assert not is_integer(timedelta(1000))
         assert not is_integer(Timedelta("1 days"))
-
-        # questionable
-        assert is_integer(np.timedelta64(1, "D"))
+        assert not is_integer(np.timedelta64(1, "D"))
 
     def test_is_float(self):
         assert is_float(1.1)