cleanup order of operations kludges (#19895)

Author: jbrockmendel

doc/source/whatsnew/v0.23.0.txt

@@ -586,6 +586,7 @@ Datetimelike API Changes
 - Operations between a :class:`Series` with dtype ``dtype='datetime64[ns]'`` and a :class:`PeriodIndex` will correctly raises ``TypeError`` (:issue:`18850`)
 - Subtraction of :class:`Series` with timezone-aware ``dtype='datetime64[ns]'`` with mis-matched timezones will raise ``TypeError`` instead of ``ValueError`` (:issue:`18817`)
 - :func:`pandas.merge` provides a more informative error message when trying to merge on timezone-aware and timezone-naive columns (:issue:`15800`)
+- For :class:`DatetimeIndex` and :class:`TimedeltaIndex` with ``freq=None``, addition or subtraction of integer-dtyped array or ``Index`` will raise ``NullFrequencyError`` instead of ``TypeError`` (:issue:`19895`)
 
 .. _whatsnew_0230.api.other:
 

pandas/core/indexes/datetimelike.py

@@ -32,6 +32,7 @@
     is_object_dtype,
     is_string_dtype,
     is_datetime64_dtype,
+    is_datetime64tz_dtype,
     is_period_dtype,
     is_timedelta64_dtype)
 from pandas.core.dtypes.generic import (
@@ -200,8 +201,9 @@ def _evaluate_compare(self, other, op):
         if is_bool_dtype(result):
             result[mask] = False
             return result
+
+        result[mask] = iNaT
         try:
-            result[mask] = iNaT
             return Index(result)
         except TypeError:
             return result
@@ -349,7 +351,7 @@ def _nat_new(self, box=True):
             return result
 
         attribs = self._get_attributes_dict()
-        if not isinstance(self, ABCPeriodIndex):
+        if not is_period_dtype(self):
             attribs['freq'] = None
         return self._simple_new(result, **attribs)
 
@@ -631,9 +633,9 @@ def _convert_scalar_indexer(self, key, kind=None):
                 ._convert_scalar_indexer(key, kind=kind))
 
     def _add_datelike(self, other):
-        raise TypeError("cannot add {0} and {1}"
-                        .format(type(self).__name__,
-                                type(other).__name__))
+        raise TypeError("cannot add {cls} and {typ}"
+                        .format(cls=type(self).__name__,
+                                typ=type(other).__name__))
 
     def _sub_datelike(self, other):
         raise com.AbstractMethodError(self)
@@ -677,7 +679,7 @@ def _add_datetimelike_methods(cls):
         """
 
         def __add__(self, other):
-            from pandas import Index, DatetimeIndex, TimedeltaIndex, DateOffset
+            from pandas import DateOffset
 
             other = lib.item_from_zerodim(other)
             if isinstance(other, ABCSeries):
@@ -700,18 +702,9 @@ def __add__(self, other):
             elif is_offsetlike(other):
                 # Array/Index of DateOffset objects
                 result = self._addsub_offset_array(other, operator.add)
-            elif isinstance(self, TimedeltaIndex) and isinstance(other, Index):
-                if hasattr(other, '_add_delta'):
-                    # i.e. DatetimeIndex, TimedeltaIndex, or PeriodIndex
-                    result = other._add_delta(self)
-                else:
-                    raise TypeError("cannot add TimedeltaIndex and {typ}"
-                                    .format(typ=type(other)))
-            elif isinstance(other, Index):
-                result = self._add_datelike(other)
-            elif is_datetime64_dtype(other):
-                # ndarray[datetime64]; note DatetimeIndex is caught above
-                return self + DatetimeIndex(other)
+            elif is_datetime64_dtype(other) or is_datetime64tz_dtype(other):
+                # DatetimeIndex, ndarray[datetime64]
+                return self._add_datelike(other)
             elif is_integer_dtype(other) and self.freq is None:
                 # GH#19123
                 raise NullFrequencyError("Cannot shift with no freq")
@@ -731,7 +724,7 @@ def __radd__(self, other):
         cls.__radd__ = __radd__
 
         def __sub__(self, other):
-            from pandas import Index, DatetimeIndex, TimedeltaIndex, DateOffset
+            from pandas import Index, DateOffset
 
             other = lib.item_from_zerodim(other)
             if isinstance(other, ABCSeries):
@@ -756,20 +749,13 @@ def __sub__(self, other):
             elif is_offsetlike(other):
                 # Array/Index of DateOffset objects
                 result = self._addsub_offset_array(other, operator.sub)
-            elif isinstance(self, TimedeltaIndex) and isinstance(other, Index):
-                # We checked above for timedelta64_dtype(other) so this
-                # must be invalid.
-                raise TypeError("cannot subtract TimedeltaIndex and {typ}"
-                                .format(typ=type(other).__name__))
-            elif isinstance(other, DatetimeIndex):
+            elif is_datetime64_dtype(other) or is_datetime64tz_dtype(other):
+                # DatetimeIndex, ndarray[datetime64]
                 result = self._sub_datelike(other)
-            elif is_datetime64_dtype(other):
-                # ndarray[datetime64]; note we caught DatetimeIndex earlier
-                return self - DatetimeIndex(other)
             elif isinstance(other, Index):
-                raise TypeError("cannot subtract {typ1} and {typ2}"
-                                .format(typ1=type(self).__name__,
-                                        typ2=type(other).__name__))
+                raise TypeError("cannot subtract {cls} and {typ}"
+                                .format(cls=type(self).__name__,
+                                        typ=type(other).__name__))
             elif is_integer_dtype(other) and self.freq is None:
                 # GH#19123
                 raise NullFrequencyError("Cannot shift with no freq")

pandas/core/indexes/datetimes.py

@@ -864,11 +864,16 @@ def _add_datelike(self, other):
     def _sub_datelike(self, other):
         # subtract a datetime from myself, yielding a TimedeltaIndex
         from pandas import TimedeltaIndex
-        if isinstance(other, DatetimeIndex):
+
+        if isinstance(other, (DatetimeIndex, np.ndarray)):
+            # if other is an ndarray, we assume it is datetime64-dtype
+            other = DatetimeIndex(other)
+
             # require tz compat
             if not self._has_same_tz(other):
-                raise TypeError("DatetimeIndex subtraction must have the same "
-                                "timezones or no timezones")
+                raise TypeError("{cls} subtraction must have the same "
+                                "timezones or no timezones"
+                                .format(cls=type(self).__name__))
             result = self._sub_datelike_dti(other)
         elif isinstance(other, (datetime, np.datetime64)):
             other = Timestamp(other)
@@ -885,8 +890,9 @@ def _sub_datelike(self, other):
                 result = self._maybe_mask_results(result,
                                                   fill_value=libts.iNaT)
         else:
-            raise TypeError("cannot subtract DatetimeIndex and {typ}"
-                            .format(typ=type(other).__name__))
+            raise TypeError("cannot subtract {cls} and {typ}"
+                            .format(cls=type(self).__name__,
+                                    typ=type(other).__name__))
         return TimedeltaIndex(result)
 
     def _sub_datelike_dti(self, other):

pandas/core/indexes/timedeltas.py

@@ -59,30 +59,28 @@ def _td_index_cmp(opname, cls):
     nat_result = True if opname == '__ne__' else False
 
     def wrapper(self, other):
-        msg = "cannot compare a TimedeltaIndex with type {0}"
+        msg = "cannot compare a {cls} with type {typ}"
         func = getattr(super(TimedeltaIndex, self), opname)
         if _is_convertible_to_td(other) or other is NaT:
             try:
                 other = _to_m8(other)
             except ValueError:
                 # failed to parse as timedelta
-                raise TypeError(msg.format(type(other)))
+                raise TypeError(msg.format(cls=type(self).__name__,
+                                           typ=type(other).__name__))
             result = func(other)
             if isna(other):
                 result.fill(nat_result)
-        else:
-            if not is_list_like(other):
-                raise TypeError(msg.format(type(other)))
 
+        elif not is_list_like(other):
+            raise TypeError(msg.format(cls=type(self).__name__,
+                                       typ=type(other).__name__))
+        else:
             other = TimedeltaIndex(other).values
             result = func(other)
             result = com._values_from_object(result)
 
-            if isinstance(other, Index):
-                o_mask = other.values.view('i8') == iNaT
-            else:
-                o_mask = other.view('i8') == iNaT
-
+            o_mask = np.array(isna(other))
             if o_mask.any():
                 result[o_mask] = nat_result
 
@@ -416,9 +414,15 @@ def _evaluate_with_timedelta_like(self, other, op):
     def _add_datelike(self, other):
         # adding a timedeltaindex to a datetimelike
         from pandas import Timestamp, DatetimeIndex
+
         if other is NaT:
             # GH#19124 pd.NaT is treated like a timedelta
             return self._nat_new()
+        elif isinstance(other, (DatetimeIndex, np.ndarray)):
+            # if other is an ndarray, we assume it is datetime64-dtype
+            # defer to implementation in DatetimeIndex
+            other = DatetimeIndex(other)
+            return other + self
         else:
             other = Timestamp(other)
             i8 = self.asi8
@@ -434,7 +438,8 @@ def _sub_datelike(self, other):
         if other is NaT:
             return self._nat_new()
         else:
-            raise TypeError("cannot subtract a datelike from a TimedeltaIndex")
+            raise TypeError("cannot subtract a datelike from a {cls}"
+                            .format(cls=type(self).__name__))
 
     def _addsub_offset_array(self, other, op):
         # Add or subtract Array-like of DateOffset objects
@@ -962,8 +967,7 @@ def _is_convertible_to_index(other):
 
 
 def _is_convertible_to_td(key):
-    # TODO: Not all DateOffset objects are convertible to Timedelta
-    return isinstance(key, (DateOffset, timedelta, Timedelta,
+    return isinstance(key, (Tick, timedelta,
                             np.timedelta64, compat.string_types))
 
 

pandas/tests/indexes/datetimes/test_arithmetic.py

@@ -508,7 +508,7 @@ def test_dti_sub_tdi(self, tz):
         result = dti - tdi
         tm.assert_index_equal(result, expected)
 
-        msg = 'cannot subtract TimedeltaIndex and DatetimeIndex'
+        msg = 'cannot subtract .*TimedeltaIndex'
         with tm.assert_raises_regex(TypeError, msg):
             tdi - dti
 
@@ -531,7 +531,7 @@ def test_dti_isub_tdi(self, tz):
         result -= tdi
         tm.assert_index_equal(result, expected)
 
-        msg = 'cannot subtract TimedeltaIndex and DatetimeIndex'
+        msg = 'cannot subtract .*TimedeltaIndex'
         with tm.assert_raises_regex(TypeError, msg):
             tdi -= dti
 

pandas/tests/indexes/timedeltas/test_arithmetic.py

@@ -792,7 +792,7 @@ def test_addition_ops(self):
         pytest.raises(ValueError, lambda: tdi[0:1] + dti)
 
         # random indexes
-        pytest.raises(TypeError, lambda: tdi + Int64Index([1, 2, 3]))
+        pytest.raises(NullFrequencyError, lambda: tdi + Int64Index([1, 2, 3]))
 
         # this is a union!
         # pytest.raises(TypeError, lambda : Int64Index([1,2,3]) + tdi)