Fix incorrect exception raised by Series[datetime64] + int (#19147)

doc/source/whatsnew/v0.23.0.txt

@@ -309,6 +309,7 @@ Other API Changes
 - ``IntervalDtype`` now returns ``True`` when compared against ``'interval'`` regardless of subtype, and ``IntervalDtype.name`` now returns ``'interval'`` regardless of subtype (:issue:`18980`)
 - :func:`Series.to_csv` now accepts a ``compression`` argument that works in the same way as the ``compression`` argument in :func:`DataFrame.to_csv` (:issue:`18958`)
 - Addition or subtraction of ``NaT`` from :class:`TimedeltaIndex` will return ``TimedeltaIndex`` instead of ``DatetimeIndex`` (:issue:`19124`)
+- :func:`DatetimeIndex.shift` and :func:`TimedeltaIndex.shift` will now raise ``NullFrequencyError`` (which subclasses ``ValueError``, which was raised in older versions) when the index object frequency is ``None`` (:issue:`19147`)
 
 .. _whatsnew_0230.deprecations:
 

pandas/core/indexes/datetimelike.py

@@ -32,6 +32,7 @@
 from pandas.core import common as com, algorithms
 from pandas.core.algorithms import checked_add_with_arr
 from pandas.core.common import AbstractMethodError
+from pandas.errors import NullFrequencyError
 
 import pandas.io.formats.printing as printing
 from pandas._libs import lib, iNaT, NaT
@@ -692,6 +693,9 @@ def __add__(self, other):
                 return self._add_datelike(other)
             elif isinstance(other, Index):
                 return self._add_datelike(other)
+            elif is_integer_dtype(other) and self.freq is None:
+                # GH#19123
+                raise NullFrequencyError("Cannot shift with no freq")
             else:  # pragma: no cover
                 return NotImplemented
 
@@ -731,7 +735,9 @@ def __sub__(self, other):
                 raise TypeError("cannot subtract {typ1} and {typ2}"
                                 .format(typ1=type(self).__name__,
                                         typ2=type(other).__name__))
-
+            elif is_integer_dtype(other) and self.freq is None:
+                # GH#19123
+                raise NullFrequencyError("Cannot shift with no freq")
             else:  # pragma: no cover
                 return NotImplemented
 
@@ -831,7 +837,7 @@ def shift(self, n, freq=None):
             return self
 
         if self.freq is None:
-            raise ValueError("Cannot shift with no freq")
+            raise NullFrequencyError("Cannot shift with no freq")
 
         start = self[0] + n * self.freq
         end = self[-1] + n * self.freq

pandas/core/ops.py

@@ -20,7 +20,7 @@
 from pandas.compat import bind_method
 import pandas.core.missing as missing
 
-from pandas.errors import PerformanceWarning
+from pandas.errors import PerformanceWarning, NullFrequencyError
 from pandas.core.common import _values_from_object, _maybe_match_name
 from pandas.core.dtypes.missing import notna, isna
 from pandas.core.dtypes.common import (
@@ -672,9 +672,8 @@ def wrapper(left, right, name=name, na_op=na_op):
 
         left, right = _align_method_SERIES(left, right)
         if is_datetime64_dtype(left) or is_datetime64tz_dtype(left):
-            result = op(pd.DatetimeIndex(left), right)
+            result = dispatch_to_index_op(op, left, right, pd.DatetimeIndex)
             res_name = _get_series_op_result_name(left, right)
-            result.name = res_name  # needs to be overriden if None
             return construct_result(left, result,
                                     index=left.index, name=res_name,
                                     dtype=result.dtype)
@@ -703,6 +702,40 @@ def wrapper(left, right, name=name, na_op=na_op):
     return wrapper
 
 
+def dispatch_to_index_op(op, left, right, index_class):
+    """
+    Wrap Series left in the given index_class to delegate the operation op
+    to the index implementation.  DatetimeIndex and TimedeltaIndex perform
+    type checking, timezone handling, overflow checks, etc.
+
+    Parameters
+    ----------
+    op : binary operator (operator.add, operator.sub, ...)
+    left : Series
+    right : object
+    index_class : DatetimeIndex or TimedeltaIndex
+
+    Returns
+    -------
+    result : object, usually DatetimeIndex, TimedeltaIndex, or Series
+    """
+    left_idx = index_class(left)
+
+    # avoid accidentally allowing integer add/sub.  For datetime64[tz] dtypes,
+    # left_idx may inherit a freq from a cached DatetimeIndex.
+    # See discussion in GH#19147.
+    if left_idx.freq is not None:
+        left_idx = left_idx._shallow_copy(freq=None)
+    try:
+        result = op(left_idx, right)
+    except NullFrequencyError:
+        # DatetimeIndex and TimedeltaIndex with freq == None raise ValueError
+        # on add/sub of integers (or int-like).  We re-raise as a TypeError.
+        raise TypeError('incompatible type for a datetime/timedelta '
+                        'operation [{name}]'.format(name=op.__name__))
+    return result
+
+
 def _get_series_op_result_name(left, right):
     # `left` is always a pd.Series
     if isinstance(right, (ABCSeries, pd.Index)):

pandas/errors/__init__.py

@@ -67,5 +67,13 @@ class MergeError(ValueError):
     """
 
 
+class NullFrequencyError(ValueError):
+    """
+    Error raised when a null `freq` attribute is used in an operation
+    that needs a non-null frequency, particularly `DatetimeIndex.shift`,
+    `TimedeltaIndex.shift`, `PeriodIndex.shift`.
+    """
+
+
 class AccessorRegistrationWarning(Warning):
     """Warning for attribute conflicts in accessor registration."""

pandas/tests/indexes/datetimes/test_ops.py

@@ -7,6 +7,7 @@
 
 from itertools import product
 import pandas as pd
+from pandas.errors import NullFrequencyError
 import pandas._libs.tslib as tslib
 from pandas._libs.tslibs.offsets import shift_months
 import pandas.util.testing as tm
@@ -593,6 +594,12 @@ def test_nat_new(self):
         exp = np.array([tslib.iNaT] * 5, dtype=np.int64)
         tm.assert_numpy_array_equal(result, exp)
 
+    def test_shift_no_freq(self):
+        # GH#19147
+        dti = pd.DatetimeIndex(['2011-01-01 10:00', '2011-01-01'], freq=None)
+        with pytest.raises(NullFrequencyError):
+            dti.shift(2)
+
     def test_shift(self):
         # GH 9903
         for tz in self.tz:

pandas/tests/indexes/timedeltas/test_timedelta.py

@@ -4,6 +4,7 @@
 from datetime import timedelta
 
 import pandas as pd
+from pandas.errors import NullFrequencyError
 import pandas.util.testing as tm
 from pandas import (timedelta_range, date_range, Series, Timedelta,
                     TimedeltaIndex, Index, DataFrame,
@@ -50,6 +51,12 @@ def test_shift(self):
                                    '10 days 01:00:03'], freq='D')
         tm.assert_index_equal(result, expected)
 
+    def test_shift_no_freq(self):
+        # GH#19147
+        tdi = TimedeltaIndex(['1 days 01:00:00', '2 days 01:00:00'], freq=None)
+        with pytest.raises(NullFrequencyError):
+            tdi.shift(2)
+
     def test_pickle_compat_construction(self):
         pass
 

pandas/tests/series/test_operators.py

@@ -693,6 +693,25 @@ def test_td64series_rsub_int_series_invalid(self, tdser):
         with pytest.raises(TypeError):
             Series([2, 3, 4]) - tdser
 
+    def test_td64_series_add_intlike(self):
+        # GH#19123
+        tdi = pd.TimedeltaIndex(['59 days', '59 days', 'NaT'])
+        ser = Series(tdi)
+
+        other = Series([20, 30, 40], dtype='uint8')
+
+        pytest.raises(TypeError, ser.__add__, 1)
+        pytest.raises(TypeError, ser.__sub__, 1)
+
+        pytest.raises(TypeError, ser.__add__, other)
+        pytest.raises(TypeError, ser.__sub__, other)
+
+        pytest.raises(TypeError, ser.__add__, other.values)
+        pytest.raises(TypeError, ser.__sub__, other.values)
+
+        pytest.raises(TypeError, ser.__add__, pd.Index(other))
+        pytest.raises(TypeError, ser.__sub__, pd.Index(other))
+
     @pytest.mark.parametrize('scalar', [1, 1.5, np.array(2)])
     def test_td64series_add_sub_numeric_scalar_invalid(self, scalar, tdser):
         with pytest.raises(TypeError):
@@ -1533,6 +1552,26 @@ def test_dt64_series_arith_overflow(self):
         res = dt - ser
         tm.assert_series_equal(res, -expected)
 
+    @pytest.mark.parametrize('tz', [None, 'Asia/Tokyo'])
+    def test_dt64_series_add_intlike(self, tz):
+        # GH#19123
+        dti = pd.DatetimeIndex(['2016-01-02', '2016-02-03', 'NaT'], tz=tz)
+        ser = Series(dti)
+
+        other = Series([20, 30, 40], dtype='uint8')
+
+        pytest.raises(TypeError, ser.__add__, 1)
+        pytest.raises(TypeError, ser.__sub__, 1)
+
+        pytest.raises(TypeError, ser.__add__, other)
+        pytest.raises(TypeError, ser.__sub__, other)
+
+        pytest.raises(TypeError, ser.__add__, other.values)
+        pytest.raises(TypeError, ser.__sub__, other.values)
+
+        pytest.raises(TypeError, ser.__add__, pd.Index(other))
+        pytest.raises(TypeError, ser.__sub__, pd.Index(other))
+
 
 class TestSeriesOperators(TestData):
     def test_op_method(self):

pandas/tests/series/test_timeseries.py

@@ -11,6 +11,8 @@
 import pandas.util._test_decorators as td
 from pandas._libs.tslib import iNaT
 from pandas.compat import lrange, StringIO, product
+from pandas.errors import NullFrequencyError
+
 from pandas.core.indexes.timedeltas import TimedeltaIndex
 from pandas.core.indexes.datetimes import DatetimeIndex
 from pandas.tseries.offsets import BDay, BMonthEnd
@@ -123,7 +125,7 @@ def test_shift2(self):
         tm.assert_index_equal(result.index, exp_index)
 
         idx = DatetimeIndex(['2000-01-01', '2000-01-02', '2000-01-04'])
-        pytest.raises(ValueError, idx.shift, 1)
+        pytest.raises(NullFrequencyError, idx.shift, 1)
 
     def test_shift_dst(self):
         # GH 13926