DEPR: object inference in to_stata

Author: jbrockmendel

pandas/io/stata.py

@@ -429,6 +429,14 @@ def parse_dates_safe(
                 d["days"] = days_in_ns // NS_PER_DAY
 
         elif infer_dtype(dates, skipna=False) == "datetime":
+            # - Deprecated casting object-dtype columns of datetimes to datetime64 when writing to stata; call df=df.infer_objects() before writing to stata instead (:issue:`??`)
+            warnings.warn(
+                "Converting object-dtype columns of datetimes to datetime64 when "
+                "writing to stata is deprecated. Call "
+                "`df=df.infer_objects(copy=False)` before writing to stata instead.",
+                FutureWarning,
+                stacklevel=find_stack_level(),
+            )
             if delta:
                 delta = dates._values - stata_epoch
 

pandas/tests/io/test_stata.py

@@ -885,7 +885,12 @@ def test_big_dates(self, datapath):
         # {c : c[-2:] for c in columns}
         with tm.ensure_clean() as path:
             expected.index.name = "index"
-            expected.to_stata(path, convert_dates=date_conversion)
+            msg = (
+                "Converting object-dtype columns of datetimes to datetime64 "
+                "when writing to stata is deprecated"
+            )
+            with tm.assert_produces_warning(FutureWarning, match=msg):
+                expected.to_stata(path, convert_dates=date_conversion)
             written_and_read_again = self.read_dta(path)
 
         tm.assert_frame_equal(