Fix len one list dataframe constructor bug for datetime (#43041)

* Fix len one list dataframe constructor bug for datetime

* Move whatsnew

Co-authored-by: Jeff Reback <[email protected]>

Author: phofl

doc/source/whatsnew/v1.3.3.rst

@@ -14,6 +14,7 @@ including other versions of pandas.
 
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
+- Fixed regression in :class:`DataFrame` constructor failing to broadcast for defined :class:`Index` and len one list of :class:`Timestamp` (:issue:`42810`)
 - Performance regression in :meth:`core.window.ewm.ExponentialMovingWindow.mean` (:issue:`42333`)
 -
 -

pandas/core/construction.py

@@ -550,7 +550,6 @@ def sanitize_array(
             subarr = subarr.astype(dtype, copy=copy)
         elif copy:
             subarr = subarr.copy()
-        return subarr
 
     else:
         if isinstance(data, (set, frozenset)):

pandas/tests/frame/test_constructors.py

@@ -1300,6 +1300,21 @@ def test_constructor_unequal_length_nested_list_column(self):
         with pytest.raises(ValueError, match=msg):
             DataFrame([[1, 2, 3, 4], [4, 5, 6, 7]], columns=arrays)
 
+    @pytest.mark.parametrize(
+        "data",
+        [
+            [[Timestamp("2021-01-01")]],
+            [{"x": Timestamp("2021-01-01")}],
+            {"x": [Timestamp("2021-01-01")]},
+            {"x": Timestamp("2021-01-01")},
+        ],
+    )
+    def test_constructor_one_element_data_list(self, data):
+        # GH#42810
+        result = DataFrame(data, index=[0, 1, 2], columns=["x"])
+        expected = DataFrame({"x": [Timestamp("2021-01-01")] * 3})
+        tm.assert_frame_equal(result, expected)
+
     def test_constructor_sequence_like(self):
         # GH 3783
         # collections.Sequence like