REF: move values_for_json to EA (#53680)

* REF: move values_for_json to EA

* docstring

Author: jbrockmendel

pandas/core/arrays/base.py

@@ -1678,6 +1678,19 @@ def _reduce(
     # Non-Optimized Default Methods; in the case of the private methods here,
     #  these are not guaranteed to be stable across pandas versions.
 
+    def _values_for_json(self) -> np.ndarray:
+        """
+        Specify how to render our entries in to_json.
+
+        Notes
+        -----
+        The dtype on the returned ndarray is not restricted, but for non-native
+        types that are not specifically handled in objToJSON.c, to_json is
+        liable to raise. In these cases, it may be safer to return an ndarray
+        of strings.
+        """
+        return np.asarray(self)
+
     def _hash_pandas_object(
         self, *, encoding: str, hash_key: str, categorize: bool
     ) -> npt.NDArray[np.uint64]:

pandas/core/arrays/datetimelike.py

@@ -2202,6 +2202,12 @@ def _with_freq(self, freq) -> Self:
     # --------------------------------------------------------------
     # ExtensionArray Interface
 
+    def _values_for_json(self) -> np.ndarray:
+        # Small performance bump vs the base class which calls np.asarray(self)
+        if isinstance(self.dtype, np.dtype):
+            return self._ndarray
+        return super()._values_for_json()
+
     def factorize(
         self,
         use_na_sentinel: bool = True,

pandas/core/internals/blocks.py

@@ -1638,9 +1638,6 @@ def get_values(self, dtype: DtypeObj | None = None) -> np.ndarray:
         """
         raise AbstractMethodError(self)
 
-    def values_for_json(self) -> np.ndarray:
-        raise AbstractMethodError(self)
-
 
 class EABackedBlock(Block):
     """
@@ -1885,9 +1882,6 @@ def get_values(self, dtype: DtypeObj | None = None) -> np.ndarray:
         # TODO(EA2D): reshape not needed with 2D EAs
         return np.asarray(values).reshape(self.shape)
 
-    def values_for_json(self) -> np.ndarray:
-        return np.asarray(self.values)
-
     @final
     def pad_or_backfill(
         self,
@@ -2174,9 +2168,6 @@ def get_values(self, dtype: DtypeObj | None = None) -> np.ndarray:
             return self.values.astype(_dtype_obj)
         return self.values
 
-    def values_for_json(self) -> np.ndarray:
-        return self.values
-
     @cache_readonly
     def is_numeric(self) -> bool:  # type: ignore[override]
         dtype = self.values.dtype
@@ -2231,9 +2222,6 @@ class DatetimeLikeBlock(NDArrayBackedExtensionBlock):
     is_numeric = False
     values: DatetimeArray | TimedeltaArray
 
-    def values_for_json(self) -> np.ndarray:
-        return self.values._ndarray
-
 
 class DatetimeTZBlock(DatetimeLikeBlock):
     """implement a datetime64 block with a tz attribute"""
@@ -2242,10 +2230,6 @@ class DatetimeTZBlock(DatetimeLikeBlock):
 
     __slots__ = ()
 
-    # Don't use values_for_json from DatetimeLikeBlock since it is
-    # an invalid optimization here(drop the tz)
-    values_for_json = NDArrayBackedExtensionBlock.values_for_json
-
 
 # -----------------------------------------------------------------
 # Constructor Helpers

pandas/core/internals/managers.py

@@ -1008,7 +1008,7 @@ def column_arrays(self) -> list[np.ndarray]:
 
         for blk in self.blocks:
             mgr_locs = blk._mgr_locs
-            values = blk.values_for_json()
+            values = blk.array_values._values_for_json()
             if values.ndim == 1:
                 # TODO(EA2D): special casing not needed with 2D EAs
                 result[mgr_locs[0]] = values