whatsnew

doc/source/whatsnew/v1.3.0.rst

@@ -696,6 +696,7 @@ Deprecations
 - Deprecated passing arguments (apart from ``value``) as positional in :meth:`DataFrame.fillna` and :meth:`Series.fillna` (:issue:`41485`)
 - Deprecated passing arguments as positional in :meth:`DataFrame.reset_index` (other than ``"level"``) and :meth:`Series.reset_index` (:issue:`41485`)
 - Deprecated construction of :class:`Series` or :class:`DataFrame` with ``DatetimeTZDtype`` data and ``datetime64[ns]`` dtype.  Use ``Series(data).dt.tz_localize(None)`` instead (:issue:`41555`,:issue:`33401`)
+- Deprecated behavior of :class:`Series` construction with large-integer values and small-integer dtype silently overflowing; use ``Series(data).astype(dtype)`` instead (:issue:`41734`)
 - Deprecated passing arguments as positional in :meth:`DataFrame.set_axis` and :meth:`Series.set_axis` (other than ``"labels"``) (:issue:`41485`)
 - Deprecated passing arguments as positional in :meth:`DataFrame.where` and :meth:`Series.where` (other than ``"cond"`` and ``"other"``) (:issue:`41485`)
 - Deprecated passing arguments as positional (other than ``filepath_or_buffer``) in :func:`read_csv` (:issue:`41485`)

pandas/core/dtypes/cast.py

@@ -2092,7 +2092,7 @@ def maybe_cast_to_integer_array(
         raise ValueError("Trying to coerce float values to integers")
 
     if casted.dtype < arr.dtype:
-        # e.g. [1, 200, 923442] and dtype="int8" -> overflows
+        # GH#41734 e.g. [1, 200, 923442] and dtype="int8" -> overflows
         warnings.warn(
             f"Values are too large to be losslessly cast to {dtype}. "
             "In a future version this will raise OverflowError. To retain the "

pandas/tests/series/test_constructors.py

@@ -712,7 +712,7 @@ def test_constructor_cast(self):
             Series(["a", "b", "c"], dtype=float)
 
     def test_constructor_signed_int_overflow_deprecation(self):
-        # GH#40144 disallow silent overflow
+        # GH#41734 disallow silent overflow
         msg = "Values are too large to be losslessly cast"
         with tm.assert_produces_warning(FutureWarning, match=msg):
             ser = Series([1, 200, 923442], dtype="int8")