REF: de-duplicate PeriodArray arithmetic code (pandas-dev#47826)

Author: jbrockmendel

pandas/core/arrays/period.py

@@ -14,15 +14,17 @@
 
 import numpy as np
 
-from pandas._libs import algos as libalgos
+from pandas._libs import (
+    algos as libalgos,
+    lib,
+)
 from pandas._libs.arrays import NDArrayBacked
 from pandas._libs.tslibs import (
     BaseOffset,
     NaT,
     NaTType,
     Timedelta,
     astype_overflowsafe,
-    delta_to_nanoseconds,
     dt64arr_to_periodarr as c_dt64arr_to_periodarr,
     get_unit_from_dtype,
     iNaT,
@@ -55,7 +57,6 @@
 )
 
 from pandas.core.dtypes.common import (
-    TD64NS_DTYPE,
     ensure_object,
     is_datetime64_any_dtype,
     is_datetime64_dtype,
@@ -72,7 +73,7 @@
     ABCSeries,
     ABCTimedeltaArray,
 )
-from pandas.core.dtypes.missing import notna
+from pandas.core.dtypes.missing import isna
 
 import pandas.core.algorithms as algos
 from pandas.core.arrays import datetimelike as dtl
@@ -764,30 +765,24 @@ def _add_timedeltalike_scalar(self, other):
             # We cannot add timedelta-like to non-tick PeriodArray
             raise raise_on_incompatible(self, other)
 
-        if notna(other):
-            # Convert to an integer increment of our own freq, disallowing
-            #  e.g. 30seconds if our freq is minutes.
-            try:
-                inc = delta_to_nanoseconds(other, reso=self.freq._reso, round_ok=False)
-            except ValueError as err:
-                # "Cannot losslessly convert units"
-                raise raise_on_incompatible(self, other) from err
-
-            return self._addsub_int_array_or_scalar(inc, operator.add)
+        if isna(other):
+            # i.e. np.timedelta64("NaT")
+            return super()._add_timedeltalike_scalar(other)
 
-        return super()._add_timedeltalike_scalar(other)
+        td = np.asarray(Timedelta(other).asm8)
+        return self._add_timedelta_arraylike(td)
 
     def _add_timedelta_arraylike(
         self, other: TimedeltaArray | npt.NDArray[np.timedelta64]
-    ):
+    ) -> PeriodArray:
         """
         Parameters
         ----------
         other : TimedeltaArray or ndarray[timedelta64]
 
         Returns
         -------
-        result : ndarray[int64]
+        PeriodArray
         """
         freq = self.freq
         if not isinstance(freq, Tick):
@@ -803,8 +798,12 @@ def _add_timedelta_arraylike(
                 np.asarray(other), dtype=dtype, copy=False, round_ok=False
             )
         except ValueError as err:
-            # TODO: not actually a great exception message in this case
-            raise raise_on_incompatible(self, other) from err
+            # e.g. if we have minutes freq and try to add 30s
+            # "Cannot losslessly convert units"
+            raise IncompatibleFrequency(
+                "Cannot add/subtract timedelta-like from PeriodArray that is "
+                "not an integer multiple of the PeriodArray's freq."
+            ) from err
 
         b_mask = np.isnat(delta)
 
@@ -835,31 +834,21 @@ def _check_timedeltalike_freq_compat(self, other):
         IncompatibleFrequency
         """
         assert isinstance(self.freq, Tick)  # checked by calling function
-        base_nanos = self.freq.base.nanos
+
+        dtype = np.dtype(f"m8[{self.freq._td64_unit}]")
 
         if isinstance(other, (timedelta, np.timedelta64, Tick)):
-            nanos = delta_to_nanoseconds(other)
-
-        elif isinstance(other, np.ndarray):
-            # numpy timedelta64 array; all entries must be compatible
-            assert other.dtype.kind == "m"
-            other = astype_overflowsafe(other, TD64NS_DTYPE, copy=False)
-            # error: Incompatible types in assignment (expression has type
-            # "ndarray[Any, dtype[Any]]", variable has type "int")
-            nanos = other.view("i8")  # type: ignore[assignment]
+            td = np.asarray(Timedelta(other).asm8)
         else:
-            # TimedeltaArray/Index
-            nanos = other.asi8
-
-        if np.all(nanos % base_nanos == 0):
-            # nanos being added is an integer multiple of the
-            #  base-frequency to self.freq
-            delta = nanos // base_nanos
-            # delta is the integer (or integer-array) number of periods
-            # by which will be added to self.
-            return delta
-
-        raise raise_on_incompatible(self, other)
+            td = np.asarray(other)
+
+        try:
+            delta = astype_overflowsafe(td, dtype=dtype, copy=False, round_ok=False)
+        except ValueError as err:
+            raise raise_on_incompatible(self, other) from err
+
+        delta = delta.view("i8")
+        return lib.item_from_zerodim(delta)
 
 
 def raise_on_incompatible(left, right):

pandas/tests/arithmetic/test_period.py

@@ -807,9 +807,13 @@ def test_parr_sub_td64array(self, box_with_array, tdi_freq, pi_freq):
 
         elif pi_freq == "D":
             # Tick, but non-compatible
-            msg = "Input has different freq=None from PeriodArray"
+            msg = (
+                "Cannot add/subtract timedelta-like from PeriodArray that is "
+                "not an integer multiple of the PeriodArray's freq."
+            )
             with pytest.raises(IncompatibleFrequency, match=msg):
                 pi - td64obj
+
             with pytest.raises(IncompatibleFrequency, match=msg):
                 pi[0] - td64obj
 
@@ -1107,7 +1111,15 @@ def test_parr_add_sub_timedeltalike_freq_mismatch_daily(
         rng = period_range("2014-05-01", "2014-05-15", freq="D")
         rng = tm.box_expected(rng, box_with_array)
 
-        msg = "Input has different freq(=.+)? from Period.*?\\(freq=D\\)"
+        msg = "|".join(
+            [
+                # non-timedelta-like DateOffset
+                "Input has different freq(=.+)? from Period.*?\\(freq=D\\)",
+                # timedelta/td64/Timedelta but not a multiple of 24H
+                "Cannot add/subtract timedelta-like from PeriodArray that is "
+                "not an integer multiple of the PeriodArray's freq.",
+            ]
+        )
         with pytest.raises(IncompatibleFrequency, match=msg):
             rng + other
         with pytest.raises(IncompatibleFrequency, match=msg):
@@ -1134,7 +1146,15 @@ def test_parr_add_timedeltalike_mismatched_freq_hourly(
         other = not_hourly
         rng = period_range("2014-01-01 10:00", "2014-01-05 10:00", freq="H")
         rng = tm.box_expected(rng, box_with_array)
-        msg = "Input has different freq(=.+)? from Period.*?\\(freq=H\\)"
+        msg = "|".join(
+            [
+                # non-timedelta-like DateOffset
+                "Input has different freq(=.+)? from Period.*?\\(freq=H\\)",
+                # timedelta/td64/Timedelta but not a multiple of 24H
+                "Cannot add/subtract timedelta-like from PeriodArray that is "
+                "not an integer multiple of the PeriodArray's freq.",
+            ]
+        )
 
         with pytest.raises(IncompatibleFrequency, match=msg):
             rng + other
@@ -1508,17 +1528,17 @@ def test_pi_offset_errors(self):
         )
         ser = Series(idx)
 
-        # Series op is applied per Period instance, thus error is raised
-        # from Period
+        msg = (
+            "Cannot add/subtract timedelta-like from PeriodArray that is not "
+            "an integer multiple of the PeriodArray's freq"
+        )
         for obj in [idx, ser]:
-            msg = r"Input has different freq=2H from Period.*?\(freq=D\)"
             with pytest.raises(IncompatibleFrequency, match=msg):
                 obj + pd.offsets.Hour(2)
 
             with pytest.raises(IncompatibleFrequency, match=msg):
                 pd.offsets.Hour(2) + obj
 
-            msg = r"Input has different freq=-2H from Period.*?\(freq=D\)"
             with pytest.raises(IncompatibleFrequency, match=msg):
                 obj - pd.offsets.Hour(2)