datetimelike indexes add/sub zero-dim integer arrays

doc/source/whatsnew/v0.23.0.txt

@@ -368,7 +368,7 @@ Numeric
 ^^^^^^^
 
 - Bug in :func:`Series.__sub__` subtracting a non-nanosecond ``np.datetime64`` object from a ``Series`` gave incorrect results (:issue:`7996`)
--
+- Bug in :class:`DatetimeIndex`, :class:`TimedeltaIndex` addition and subtraction of zero-dimensional integer arrays gave incrrect results (:issue:`19012`)
 -
 
 Categorical

pandas/core/dtypes/common.py

@@ -13,7 +13,7 @@
                       ABCDatetimeIndex, ABCSeries,
                       ABCSparseArray, ABCSparseSeries, ABCCategoricalIndex,
                       ABCIndexClass, ABCDateOffset)
-from .inference import is_string_like, is_list_like
+from .inference import is_string_like, is_list_like, is_zero_dim_array
 from .inference import *  # noqa
 
 
@@ -291,6 +291,8 @@ def is_offsetlike(arr_or_obj):
     """
     if isinstance(arr_or_obj, ABCDateOffset):
         return True
+    elif is_zero_dim_array(arr_or_obj):
+        return isinstance(arr_or_obj.item(), ABCDateOffset)
     elif (is_list_like(arr_or_obj) and len(arr_or_obj) and
           is_object_dtype(arr_or_obj)):
         return all(isinstance(x, ABCDateOffset) for x in arr_or_obj)

pandas/core/dtypes/inference.py

@@ -24,6 +24,22 @@
 is_interval = lib.is_interval
 
 
+def is_zero_dim_array(obj):
+    """
+    Check if this is a numpy array with dimension zero, which in some
+    cases is treated like a scalar.
+
+    Parameters
+    ----------
+    obj : object
+
+    Returns
+    -------
+    is_zero_dim_array : bool
+    """
+    return isinstance(obj, np.ndarray) and obj.ndim == 0
+
+
 def is_number(obj):
     """
     Check if the object is a number.

pandas/core/indexes/datetimelike.py

@@ -15,7 +15,7 @@
     is_dtype_equal,
     is_float,
     is_integer,
-    is_list_like,
+    is_list_like, is_zero_dim_array,
     is_scalar,
     is_bool_dtype,
     is_offsetlike,
@@ -678,7 +678,8 @@ def __add__(self, other):
                                 .format(typ=type(other)))
             elif isinstance(other, (DateOffset, timedelta)):
                 return self._add_delta(other)
-            elif is_integer(other):
+            elif is_integer(other) or (is_integer_dtype(other) and
+                                       is_zero_dim_array(other)):
                 return self.shift(other)
             elif isinstance(other, (datetime, np.datetime64)):
                 return self._add_datelike(other)
@@ -708,7 +709,8 @@ def __sub__(self, other):
                 return self._sub_datelike(other)
             elif isinstance(other, (DateOffset, timedelta)):
                 return self._add_delta(-other)
-            elif is_integer(other):
+            elif is_integer(other) or (is_integer_dtype(other) and
+                                       is_zero_dim_array(other)):
                 return self.shift(-other)
             elif isinstance(other, (datetime, np.datetime64)):
                 return self._sub_datelike(other)

pandas/tests/dtypes/test_inference.py

@@ -33,6 +33,7 @@
     is_integer,
     is_float,
     is_bool,
+    is_zero_dim_array,
     is_scalar,
     is_scipy_sparse,
     _ensure_int32,
@@ -1218,3 +1219,11 @@ def test_ensure_categorical():
     values = Categorical(values)
     result = _ensure_categorical(values)
     tm.assert_categorical_equal(result, values)
+
+
+def test_is_zero_dim_array():
+    assert not is_zero_dim_array(1)
+    assert not is_zero_dim_array(False)
+    assert not is_zero_dim_array(np.array([]))
+    assert not is_zero_dim_array(np.array([1]))
+    assert is_zero_dim_array(np.array(1))

pandas/tests/indexes/conftest.py

@@ -1,4 +1,5 @@
 import pytest
+import numpy as np
 
 import pandas.util.testing as tm
 from pandas.core.indexes.api import Index, MultiIndex
@@ -22,3 +23,9 @@
                 ids=lambda x: type(x).__name__)
 def indices(request):
     return request.param
+
+
+@pytest.fixture(params=[1, np.array(1, dtype=np.int64)])
+def one(request):
+    # zero-dim integer array behaves like an integer
+    return request.param

pandas/tests/indexes/datetimes/test_arithmetic.py

@@ -58,36 +58,37 @@ def test_dti_radd_timestamp_raises(self):
     # -------------------------------------------------------------
     # Binary operations DatetimeIndex and int
 
-    def test_dti_add_int(self, tz):
+    def test_dti_add_int(self, tz, one):
+        # Variants of `one` for #19012
         rng = pd.date_range('2000-01-01 09:00', freq='H',
                             periods=10, tz=tz)
-        result = rng + 1
+        result = rng + one
         expected = pd.date_range('2000-01-01 10:00', freq='H',
                                  periods=10, tz=tz)
         tm.assert_index_equal(result, expected)
 
-    def test_dti_iadd_int(self, tz):
+    def test_dti_iadd_int(self, tz, one):
         rng = pd.date_range('2000-01-01 09:00', freq='H',
                             periods=10, tz=tz)
         expected = pd.date_range('2000-01-01 10:00', freq='H',
                                  periods=10, tz=tz)
-        rng += 1
+        rng += one
         tm.assert_index_equal(rng, expected)
 
-    def test_dti_sub_int(self, tz):
+    def test_dti_sub_int(self, tz, one):
         rng = pd.date_range('2000-01-01 09:00', freq='H',
                             periods=10, tz=tz)
-        result = rng - 1
+        result = rng - one
         expected = pd.date_range('2000-01-01 08:00', freq='H',
                                  periods=10, tz=tz)
         tm.assert_index_equal(result, expected)
 
-    def test_dti_isub_int(self, tz):
+    def test_dti_isub_int(self, tz, one):
         rng = pd.date_range('2000-01-01 09:00', freq='H',
                             periods=10, tz=tz)
         expected = pd.date_range('2000-01-01 08:00', freq='H',
                                  periods=10, tz=tz)
-        rng -= 1
+        rng -= one
         tm.assert_index_equal(rng, expected)
 
     # -------------------------------------------------------------

pandas/tests/indexes/period/test_arithmetic.py

@@ -131,19 +131,21 @@ def test_add_iadd(self):
                     period.IncompatibleFrequency, msg):
                 rng += delta
 
-        # int
+    def test_pi_add_int(self, one):
+        # Variants of `one` for #19012
         rng = pd.period_range('2000-01-01 09:00', freq='H', periods=10)
-        result = rng + 1
+        result = rng + one
         expected = pd.period_range('2000-01-01 10:00', freq='H', periods=10)
         tm.assert_index_equal(result, expected)
-        rng += 1
+        rng += one
         tm.assert_index_equal(rng, expected)
 
-    def test_sub(self):
+    @pytest.mark.parametrize('five', [5, np.array(5, dtype=np.int64)])
+    def test_sub(self, five):
         rng = period_range('2007-01', periods=50)
 
-        result = rng - 5
-        exp = rng + (-5)
+        result = rng - five
+        exp = rng + (-five)
         tm.assert_index_equal(result, exp)
 
     def test_sub_isub(self):

pandas/tests/indexes/timedeltas/test_arithmetic.py

@@ -121,28 +121,29 @@ def test_ufunc_coercions(self):
     # -------------------------------------------------------------
     # Binary operations TimedeltaIndex and integer
 
-    def test_tdi_add_int(self):
+    def test_tdi_add_int(self, one):
+        # Variants of `one` for #19012
         rng = timedelta_range('1 days 09:00:00', freq='H', periods=10)
-        result = rng + 1
+        result = rng + one
         expected = timedelta_range('1 days 10:00:00', freq='H', periods=10)
         tm.assert_index_equal(result, expected)
 
-    def test_tdi_iadd_int(self):
+    def test_tdi_iadd_int(self, one):
         rng = timedelta_range('1 days 09:00:00', freq='H', periods=10)
         expected = timedelta_range('1 days 10:00:00', freq='H', periods=10)
-        rng += 1
+        rng += one
         tm.assert_index_equal(rng, expected)
 
-    def test_tdi_sub_int(self):
+    def test_tdi_sub_int(self, one):
         rng = timedelta_range('1 days 09:00:00', freq='H', periods=10)
-        result = rng - 1
+        result = rng - one
         expected = timedelta_range('1 days 08:00:00', freq='H', periods=10)
         tm.assert_index_equal(result, expected)
 
-    def test_tdi_isub_int(self):
+    def test_tdi_isub_int(self, one):
         rng = timedelta_range('1 days 09:00:00', freq='H', periods=10)
         expected = timedelta_range('1 days 08:00:00', freq='H', periods=10)
-        rng -= 1
+        rng -= one
         tm.assert_index_equal(rng, expected)
 
     # -------------------------------------------------------------