BUG: Fix Series(List[Interval]) to infer interval dtype (#28399)

Author: jschendel

doc/source/whatsnew/v1.0.0.rst

@@ -885,6 +885,7 @@ Interval
 
 - Bug in :meth:`IntervalIndex.get_indexer` where a :class:`Categorical` or :class:`CategoricalIndex` ``target`` would incorrectly raise a ``TypeError`` (:issue:`30063`)
 - Bug in ``pandas.core.dtypes.cast.infer_dtype_from_scalar`` where passing ``pandas_dtype=True`` did not infer :class:`IntervalDtype` (:issue:`30337`)
+- Bug in :class:`Series` constructor where constructing a ``Series`` from a ``list`` of :class:`Interval` objects resulted in ``object`` dtype instead of :class:`IntervalDtype` (:issue:`23563`)
 - Bug in :class:`IntervalDtype` where the ``kind`` attribute was incorrectly set as ``None`` instead of ``"O"`` (:issue:`30568`)
 - Bug in :class:`IntervalIndex`, :class:`~arrays.IntervalArray`, and :class:`Series` with interval data where equality comparisons were incorrect (:issue:`24112`)
 

pandas/core/construction.py

@@ -497,13 +497,8 @@ def sanitize_array(
 
         if is_object_dtype(subarr.dtype) and not is_object_dtype(dtype):
             inferred = lib.infer_dtype(subarr, skipna=False)
-            if inferred == "period":
-                from pandas.core.arrays import period_array
-
-                try:
-                    subarr = period_array(subarr)
-                except IncompatibleFrequency:
-                    pass
+            if inferred in {"interval", "period"}:
+                subarr = array(subarr)
 
     return subarr
 

pandas/tests/series/test_constructors.py

@@ -27,7 +27,7 @@
     timedelta_range,
 )
 import pandas._testing as tm
-from pandas.core.arrays import period_array
+from pandas.core.arrays import IntervalArray, period_array
 
 
 class TestSeriesConstructors:
@@ -967,16 +967,34 @@ def test_constructor_with_naive_string_and_datetimetz_dtype(self, arg):
         expected = Series(pd.Timestamp(arg)).dt.tz_localize("CET")
         tm.assert_series_equal(result, expected)
 
-    def test_construction_interval(self):
+    @pytest.mark.parametrize("interval_constructor", [IntervalIndex, IntervalArray])
+    def test_construction_interval(self, interval_constructor):
         # construction from interval & array of intervals
-        index = IntervalIndex.from_breaks(np.arange(3), closed="right")
-        result = Series(index)
-        repr(result)
-        str(result)
-        tm.assert_index_equal(Index(result.values), index)
+        intervals = interval_constructor.from_breaks(np.arange(3), closed="right")
+        result = Series(intervals)
+        assert result.dtype == "interval[int64]"
+        tm.assert_index_equal(Index(result.values), Index(intervals))
 
-        result = Series(index.values)
-        tm.assert_index_equal(Index(result.values), index)
+    @pytest.mark.parametrize(
+        "data_constructor", [list, np.array], ids=["list", "ndarray[object]"]
+    )
+    def test_constructor_infer_interval(self, data_constructor):
+        # GH 23563: consistent closed results in interval dtype
+        data = [pd.Interval(0, 1), pd.Interval(0, 2), None]
+        result = pd.Series(data_constructor(data))
+        expected = pd.Series(IntervalArray(data))
+        assert result.dtype == "interval[float64]"
+        tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "data_constructor", [list, np.array], ids=["list", "ndarray[object]"]
+    )
+    def test_constructor_interval_mixed_closed(self, data_constructor):
+        # GH 23563: mixed closed results in object dtype (not interval dtype)
+        data = [pd.Interval(0, 1, closed="both"), pd.Interval(0, 2, closed="neither")]
+        result = Series(data_constructor(data))
+        assert result.dtype == object
+        assert result.tolist() == data
 
     def test_construction_consistency(self):
 
@@ -993,17 +1011,16 @@ def test_construction_consistency(self):
         result = Series(s.values, dtype=s.dtype)
         tm.assert_series_equal(result, s)
 
-    def test_constructor_infer_period(self):
+    @pytest.mark.parametrize(
+        "data_constructor", [list, np.array], ids=["list", "ndarray[object]"]
+    )
+    def test_constructor_infer_period(self, data_constructor):
         data = [pd.Period("2000", "D"), pd.Period("2001", "D"), None]
-        result = pd.Series(data)
+        result = pd.Series(data_constructor(data))
         expected = pd.Series(period_array(data))
         tm.assert_series_equal(result, expected)
         assert result.dtype == "Period[D]"
 
-        data = np.asarray(data, dtype=object)
-        tm.assert_series_equal(result, expected)
-        assert result.dtype == "Period[D]"
-
     def test_constructor_period_incompatible_frequency(self):
         data = [pd.Period("2000", "D"), pd.Period("2001", "A")]
         result = pd.Series(data)