REF: use _wrap_joined_index in PeriodIndex.join (pandas-dev#33736)

Author: jbrockmendel

pandas/core/indexes/datetimelike.py

@@ -2,7 +2,7 @@
 Base and utility classes for tseries type pandas objects.
 """
 from datetime import datetime
-from typing import Any, List, Optional, Union
+from typing import Any, List, Optional, Union, cast
 
 import numpy as np
 
@@ -583,6 +583,22 @@ def delete(self, loc):
         arr = type(self._data)._simple_new(new_i8s, dtype=self.dtype, freq=freq)
         return type(self)._simple_new(arr, name=self.name)
 
+    # --------------------------------------------------------------------
+    # Join/Set Methods
+
+    def _wrap_joined_index(self, joined: np.ndarray, other):
+        assert other.dtype == self.dtype, (other.dtype, self.dtype)
+        name = get_op_result_name(self, other)
+
+        if is_period_dtype(self.dtype):
+            freq = self.freq
+        else:
+            self = cast(DatetimeTimedeltaMixin, self)
+            freq = self.freq if self._can_fast_union(other) else None
+        new_data = type(self._data)._simple_new(joined, dtype=self.dtype, freq=freq)
+
+        return type(self)._simple_new(new_data, name=name)
+
 
 class DatetimeTimedeltaMixin(DatetimeIndexOpsMixin, Int64Index):
     """
@@ -878,15 +894,6 @@ def _is_convertible_to_index_for_join(cls, other: Index) -> bool:
             return True
         return False
 
-    def _wrap_joined_index(self, joined: np.ndarray, other):
-        assert other.dtype == self.dtype, (other.dtype, self.dtype)
-        name = get_op_result_name(self, other)
-
-        freq = self.freq if self._can_fast_union(other) else None
-        new_data = type(self._data)._simple_new(joined, dtype=self.dtype, freq=freq)
-
-        return type(self)._simple_new(new_data, name=name)
-
     # --------------------------------------------------------------------
     # List-Like Methods
 

pandas/core/indexes/period.py

@@ -628,6 +628,7 @@ def join(self, other, how="left", level=None, return_indexers=False, sort=False)
                 other, how=how, level=level, return_indexers=return_indexers, sort=sort
             )
 
+        # _assert_can_do_setop ensures we have matching dtype
         result = Int64Index.join(
             self,
             other,
@@ -636,11 +637,7 @@ def join(self, other, how="left", level=None, return_indexers=False, sort=False)
             return_indexers=return_indexers,
             sort=sort,
         )
-
-        if return_indexers:
-            result, lidx, ridx = result
-            return self._apply_meta(result), lidx, ridx
-        return self._apply_meta(result)
+        return result
 
     # ------------------------------------------------------------------------
     # Set Operation Methods
@@ -719,13 +716,6 @@ def _union(self, other, sort):
 
     # ------------------------------------------------------------------------
 
-    def _apply_meta(self, rawarr) -> "PeriodIndex":
-        if not isinstance(rawarr, PeriodIndex):
-            if not isinstance(rawarr, PeriodArray):
-                rawarr = PeriodArray(rawarr, freq=self.freq)
-            rawarr = PeriodIndex._simple_new(rawarr, name=self.name)
-        return rawarr
-
     def memory_usage(self, deep=False):
         result = super().memory_usage(deep=deep)
         if hasattr(self, "_cache") and "_int64index" in self._cache: