REF: avoid accessing internals in io.formats.csv (#55446)

* REF: to_native_types->get_values_for_csv, make kwargs explicit

* REF: avoid internals in to_csv

Author: jbrockmendel

pandas/core/frame.py

@@ -1323,6 +1323,25 @@ def to_string(
                 line_width=line_width,
             )
 
+    def _get_values_for_csv(
+        self,
+        *,
+        float_format: FloatFormatType | None,
+        date_format: str | None,
+        decimal: str,
+        na_rep: str,
+        quoting,  # int csv.QUOTE_FOO from stdlib
+    ) -> Self:
+        # helper used by to_csv
+        mgr = self._mgr.get_values_for_csv(
+            float_format=float_format,
+            date_format=date_format,
+            decimal=decimal,
+            na_rep=na_rep,
+            quoting=quoting,
+        )
+        return self._constructor_from_mgr(mgr, axes=mgr.axes)
+
     # ----------------------------------------------------------------------
 
     @property

pandas/core/internals/array_manager.py

@@ -79,9 +79,9 @@
     ensure_block_shape,
     external_values,
     extract_pandas_array,
+    get_values_for_csv,
     maybe_coerce_values,
     new_block,
-    to_native_types,
 )
 from pandas.core.internals.managers import make_na_array
 
@@ -343,8 +343,17 @@ def _convert(arr):
 
         return self.apply(_convert)
 
-    def to_native_types(self, **kwargs) -> Self:
-        return self.apply(to_native_types, **kwargs)
+    def get_values_for_csv(
+        self, *, float_format, date_format, decimal, na_rep: str = "nan", quoting=None
+    ) -> Self:
+        return self.apply(
+            get_values_for_csv,
+            na_rep=na_rep,
+            quoting=quoting,
+            float_format=float_format,
+            date_format=date_format,
+            decimal=decimal,
+        )
 
     @property
     def any_extension_types(self) -> bool:

pandas/core/internals/blocks.py

@@ -692,9 +692,18 @@ def astype(
         return newb
 
     @final
-    def to_native_types(self, na_rep: str = "nan", quoting=None, **kwargs) -> Block:
+    def get_values_for_csv(
+        self, *, float_format, date_format, decimal, na_rep: str = "nan", quoting=None
+    ) -> Block:
         """convert to our native types format"""
-        result = to_native_types(self.values, na_rep=na_rep, quoting=quoting, **kwargs)
+        result = get_values_for_csv(
+            self.values,
+            na_rep=na_rep,
+            quoting=quoting,
+            float_format=float_format,
+            date_format=date_format,
+            decimal=decimal,
+        )
         return self.make_block(result)
 
     @final
@@ -2593,14 +2602,14 @@ def ensure_block_shape(values: ArrayLike, ndim: int = 1) -> ArrayLike:
     return values
 
 
-def to_native_types(
+def get_values_for_csv(
     values: ArrayLike,
     *,
+    date_format,
     na_rep: str = "nan",
     quoting=None,
     float_format=None,
     decimal: str = ".",
-    **kwargs,
 ) -> npt.NDArray[np.object_]:
     """convert to our native types format"""
     if isinstance(values, Categorical) and values.categories.dtype.kind in "Mm":
@@ -2615,14 +2624,16 @@ def to_native_types(
 
     if isinstance(values, (DatetimeArray, TimedeltaArray)):
         if values.ndim == 1:
-            result = values._format_native_types(na_rep=na_rep, **kwargs)
+            result = values._format_native_types(na_rep=na_rep, date_format=date_format)
             result = result.astype(object, copy=False)
             return result
 
         # GH#21734 Process every column separately, they might have different formats
         results_converted = []
         for i in range(len(values)):
-            result = values[i, :]._format_native_types(na_rep=na_rep, **kwargs)
+            result = values[i, :]._format_native_types(
+                na_rep=na_rep, date_format=date_format
+            )
             results_converted.append(result.astype(object, copy=False))
         return np.vstack(results_converted)
 

pandas/core/internals/managers.py

@@ -430,12 +430,21 @@ def convert(self, copy: bool | None) -> Self:
 
         return self.apply("convert", copy=copy, using_cow=using_copy_on_write())
 
-    def to_native_types(self, **kwargs) -> Self:
+    def get_values_for_csv(
+        self, *, float_format, date_format, decimal, na_rep: str = "nan", quoting=None
+    ) -> Self:
         """
         Convert values to native types (strings / python objects) that are used
         in formatting (repr / csv).
         """
-        return self.apply("to_native_types", **kwargs)
+        return self.apply(
+            "get_values_for_csv",
+            na_rep=na_rep,
+            quoting=quoting,
+            float_format=float_format,
+            date_format=date_format,
+            decimal=decimal,
+        )
 
     @property
     def any_extension_types(self) -> bool:

pandas/io/formats/csvs.py

@@ -314,8 +314,8 @@ def _save_chunk(self, start_i: int, end_i: int) -> None:
         slicer = slice(start_i, end_i)
         df = self.obj.iloc[slicer]
 
-        res = df._mgr.to_native_types(**self._number_format)
-        data = [res.iget_values(i) for i in range(len(res.items))]
+        res = df._get_values_for_csv(**self._number_format)
+        data = list(res._iter_column_arrays())
 
         ix = self.data_index[slicer]._format_native_types(**self._number_format)
         libwriters.write_csv_rows(