REF: share fillna TDBlock/DTBlock (#39893)

Author: jbrockmendel

pandas/core/internals/blocks.py

@@ -2048,6 +2048,21 @@ def shift(self, periods: int, axis: int = 0, fill_value: Any = None) -> List[Blo
         new_values = values.shift(periods, fill_value=fill_value, axis=axis)
         return [self.make_block_same_class(new_values)]
 
+    def fillna(
+        self, value, limit=None, inplace: bool = False, downcast=None
+    ) -> List[Block]:
+
+        if not self._can_hold_element(value) and self.dtype.kind != "m":
+            # We support filling a DatetimeTZ with a `value` whose timezone
+            #  is different by coercing to object.
+            # TODO: don't special-case td64
+            return self.astype(object).fillna(value, limit, inplace, downcast)
+
+        values = self.array_values()
+        values = values if inplace else values.copy()
+        new_values = values.fillna(value=value, limit=limit)
+        return [self.make_block_same_class(values=new_values)]
+
 
 class DatetimeLikeBlockMixin(NDArrayBackedExtensionBlock):
     """Mixin class for DatetimeBlock, DatetimeTZBlock, and TimedeltaBlock."""
@@ -2134,6 +2149,7 @@ class DatetimeTZBlock(ExtensionBlock, DatetimeBlock):
     fill_value = NaT
     where = DatetimeBlock.where
     putmask = DatetimeLikeBlockMixin.putmask
+    fillna = DatetimeLikeBlockMixin.fillna
 
     array_values = ExtensionBlock.array_values
 
@@ -2172,19 +2188,6 @@ def external_values(self):
         # Avoid FutureWarning in .astype in casting from dt64tz to dt64
         return self.values._data
 
-    def fillna(
-        self, value, limit=None, inplace: bool = False, downcast=None
-    ) -> List[Block]:
-        # We support filling a DatetimeTZ with a `value` whose timezone
-        # is different by coercing to object.
-        if self._can_hold_element(value):
-            return super().fillna(value, limit, inplace, downcast)
-
-        # different timezones, or a non-tz
-        return self.astype(object).fillna(
-            value, limit=limit, inplace=inplace, downcast=downcast
-        )
-
 
 class TimeDeltaBlock(DatetimeLikeBlockMixin):
     __slots__ = ()
@@ -2194,14 +2197,6 @@ class TimeDeltaBlock(DatetimeLikeBlockMixin):
     fill_value = np.timedelta64("NaT", "ns")
     _dtype = fill_value.dtype
 
-    def fillna(
-        self, value, limit=None, inplace: bool = False, downcast=None
-    ) -> List[Block]:
-        values = self.array_values()
-        values = values if inplace else values.copy()
-        new_values = values.fillna(value=value, limit=limit)
-        return [self.make_block_same_class(values=new_values)]
-
 
 class ObjectBlock(Block):
     __slots__ = ()