BUG: pandas.to_datetime raises exception when more than 50 values needs coercion to NaT (#43732)

pandas/core/arrays/datetimes.py

@@ -2223,14 +2223,14 @@ def objects_to_datetime64ns(
             allow_mixed=allow_mixed,
         )
         result = result.reshape(data.shape, order=order)
-    except ValueError as err:
+    except ValueError:
         try:
             values, tz_parsed = conversion.datetime_to_datetime64(data.ravel("K"))
             # If tzaware, these values represent unix timestamps, so we
             #  return them as i8 to distinguish from wall times
             values = values.reshape(data.shape, order=order)
             return values.view("i8"), tz_parsed
-        except (ValueError, TypeError):
+        except (ValueError, TypeError) as err:
             raise err
 
     if tz_parsed is not None:

pandas/core/tools/datetimes.py

@@ -164,6 +164,7 @@ def _maybe_cache(
     format: str | None,
     cache: bool,
     convert_listlike: Callable,
+    errors: str = "raise",
 ) -> Series:
     """
     Create a cache of unique dates from an array of dates
@@ -177,6 +178,10 @@ def _maybe_cache(
         True attempts to create a cache of converted values
     convert_listlike : function
         Conversion function to apply on dates
+    errors : {'ignore', 'raise', 'coerce'}, default 'raise'
+        - If 'raise', then invalid parsing will raise an exception.
+        - If 'coerce', then invalid parsing will be set as NaT.
+        - If 'ignore', then invalid parsing will return the input.
 
     Returns
     -------
@@ -195,7 +200,16 @@ def _maybe_cache(
         unique_dates = unique(arg)
         if len(unique_dates) < len(arg):
             cache_dates = convert_listlike(unique_dates, format)
-            cache_array = Series(cache_dates, index=unique_dates)
+            try:
+                cache_array = Series(cache_dates, index=unique_dates)
+            except OutOfBoundsDatetime:
+                # caching attempts to create a DatetimeIndex, which may raise
+                # an OOB. If that's the desired behavior, then just reraise...
+                if errors == "raise":
+                    raise
+                # ... otherwise, continue without the cache.
+                return cache_array
+
             # GH#39882 and GH#35888 in case of None and NaT we get duplicates
             if not cache_array.index.is_unique:
                 cache_array = cache_array[~cache_array.index.duplicated()]
@@ -893,32 +907,25 @@ def to_datetime(
             else:
                 result = arg.tz_localize(tz)
     elif isinstance(arg, ABCSeries):
-        cache_array = _maybe_cache(arg, format, cache, convert_listlike)
+        cache_array = _maybe_cache(arg, format, cache, convert_listlike, errors)
+
         if not cache_array.empty:
             result = arg.map(cache_array)
         else:
-            values = convert_listlike(arg._values, format)
+            values = convert_listlike(arg._values, format, errors)
             result = arg._constructor(values, index=arg.index, name=arg.name)
     elif isinstance(arg, (ABCDataFrame, abc.MutableMapping)):
         result = _assemble_from_unit_mappings(arg, errors, tz)
     elif isinstance(arg, Index):
-        cache_array = _maybe_cache(arg, format, cache, convert_listlike)
+        cache_array = _maybe_cache(arg, format, cache, convert_listlike, errors)
+
         if not cache_array.empty:
             result = _convert_and_box_cache(arg, cache_array, name=arg.name)
         else:
             result = convert_listlike(arg, format, name=arg.name)
     elif is_list_like(arg):
-        try:
-            cache_array = _maybe_cache(arg, format, cache, convert_listlike)
-        except OutOfBoundsDatetime:
-            # caching attempts to create a DatetimeIndex, which may raise
-            # an OOB. If that's the desired behavior, then just reraise...
-            if errors == "raise":
-                raise
-            # ... otherwise, continue without the cache.
-            from pandas import Series
+        cache_array = _maybe_cache(arg, format, cache, convert_listlike, errors)
 
-            cache_array = Series([], dtype=object)  # just an empty array
         if not cache_array.empty:
             result = _convert_and_box_cache(arg, cache_array)
         else:

pandas/tests/tools/test_to_datetime.py

@@ -7,6 +7,7 @@
     timedelta,
 )
 from decimal import Decimal
+from functools import partial
 import locale
 
 from dateutil.parser import parse
@@ -992,6 +993,30 @@ def test_convert_object_to_datetime_with_cache(
         )
         tm.assert_series_equal(result_series, expected_series)
 
+    @pytest.mark.parametrize(
+        "constructor",
+        (
+            partial(Series, dtype="object"),
+            list,
+            np.array,
+        ),
+    )
+    @pytest.mark.parametrize(
+        "datetimelikes,expected_values",
+        (datetime(3000, 1, 1, 0, 0, 0, 0, pytz.UTC), NaT),
+    )
+    def test_convert_object_to_datetime_nat_utc(
+        self, cache, datetimelikes, expected_values, constructor
+    ):
+        # GH#43732
+        res = constructor(datetimelikes * (start_caching_at + 1))
+        result_series = Series(to_datetime(res, errors="coerce", cache=cache, utc=True))
+        expected_series = Series(
+            (expected_values * (start_caching_at + 1)),
+            dtype="datetime64[ns, UTC]",
+        )
+        tm.assert_series_equal(result_series, expected_series)
+
     @pytest.mark.parametrize(
         "date, format",
         [