BUG: Series construction with EA dtype and index but no data fails

doc/source/whatsnew/v1.1.0.rst

@@ -732,7 +732,7 @@ ExtensionArray
 ^^^^^^^^^^^^^^
 
 - Fixed bug where :meth:`Series.value_counts` would raise on empty input of ``Int64`` dtype (:issue:`33317`)
--
+- Fixed bug in :class:`Series` construction with EA dtype and index but no data or scalar data fails (:issue:`26469`)
 
 
 Other

pandas/core/construction.py

@@ -516,7 +516,7 @@ def _try_cast(
 
     Parameters
     ----------
-    arr : ndarray, list, tuple, iterator (catchall)
+    arr : ndarray, scalar, list, tuple, iterator (catchall)
         Excludes: ExtensionArray, Series, Index.
     dtype : np.dtype, ExtensionDtype or None
     copy : bool
@@ -533,6 +533,10 @@ def _try_cast(
     if isinstance(dtype, ExtensionDtype) and dtype.kind != "M":
         # create an extension array from its dtype
         # DatetimeTZ case needs to go through maybe_cast_to_datetime
+
+        if lib.is_scalar(arr):
+            arr = [arr]
+
         array_type = dtype.construct_array_type()._from_sequence
         subarr = array_type(arr, dtype=dtype, copy=copy)
         return subarr

pandas/tests/extension/arrow/test_bool.py

@@ -55,6 +55,16 @@ def test_from_dtype(self, data):
     def test_from_sequence_from_cls(self, data):
         super().test_from_sequence_from_cls(data)
 
+    @pytest.mark.xfail(reason="GH-26469")
+    def test_series_constructor_no_data_with_index(self, dtype, na_value):
+        # pyarrow.lib.ArrowInvalid: only handle 1-dimensional arrays
+        super().test_series_constructor_no_data_with_index(dtype, na_value)
+
+    @pytest.mark.xfail(reason="GH-26469")
+    def test_series_constructor_scalar_na_with_index(self, dtype, na_value):
+        # pyarrow.lib.ArrowInvalid: only handle 1-dimensional arrays
+        super().test_series_constructor_scalar_na_with_index(dtype, na_value)
+
 
 class TestReduce(base.BaseNoReduceTests):
     def test_reduce_series_boolean(self):

pandas/tests/extension/base/constructors.py

@@ -33,6 +33,26 @@ def test_series_constructor(self, data):
         assert result2.dtype == data.dtype
         assert isinstance(result2._mgr.blocks[0], ExtensionBlock)
 
+    def test_series_constructor_no_data_with_index(self, dtype, na_value):
+        result = pd.Series(index=[1, 2, 3], dtype=dtype)
+        expected = pd.Series([na_value] * 3, index=[1, 2, 3], dtype=dtype)
+        self.assert_series_equal(result, expected)
+
+    def test_series_constructor_scalar_na_with_index(self, dtype, na_value):
+        result = pd.Series(na_value, index=[1, 2, 3], dtype=dtype)
+        expected = pd.Series([na_value] * 3, index=[1, 2, 3], dtype=dtype)
+        self.assert_series_equal(result, expected)
+
+    def test_series_constructor_scalar_with_index(self, data, dtype):
+        scalar = data[0]
+        result = pd.Series(scalar, index=[1, 2, 3], dtype=dtype)
+        expected = pd.Series([scalar] * 3, index=[1, 2, 3], dtype=dtype)
+        self.assert_series_equal(result, expected)
+
+        result = pd.Series(scalar, index=["foo"], dtype=dtype)
+        expected = pd.Series([scalar], index=["foo"], dtype=dtype)
+        self.assert_series_equal(result, expected)
+
     @pytest.mark.parametrize("from_series", [True, False])
     def test_dataframe_constructor_from_dict(self, data, from_series):
         if from_series:

pandas/tests/extension/json/test_json.py

@@ -150,6 +150,21 @@ def test_from_dtype(self, data):
         # construct from our dtype & string dtype
         pass
 
+    @pytest.mark.xfail(reason="GH-26469")
+    def test_series_constructor_no_data_with_index(self, dtype, na_value):
+        # RecursionError: maximum recursion depth exceeded in comparison
+        super().test_series_constructor_no_data_with_index(dtype, na_value)
+
+    @pytest.mark.xfail(reason="GH-26469")
+    def test_series_constructor_scalar_na_with_index(self, dtype, na_value):
+        # RecursionError: maximum recursion depth exceeded in comparison
+        super().test_series_constructor_scalar_na_with_index(dtype, na_value)
+
+    @pytest.mark.xfail(reason="GH-26469")
+    def test_series_constructor_scalar_with_index(self, data, dtype):
+        # TypeError: All values must be of type <class 'collections.abc.Mapping'>
+        super().test_series_constructor_scalar_with_index(data, dtype)
+
 
 class TestReshaping(BaseJSON, base.BaseReshapingTests):
     @pytest.mark.skip(reason="Different definitions of NA")

pandas/tests/extension/test_datetime.py

@@ -82,7 +82,10 @@ class TestDatetimeDtype(BaseDatetimeTests, base.BaseDtypeTests):
 
 
 class TestConstructors(BaseDatetimeTests, base.BaseConstructorsTests):
-    pass
+    @pytest.mark.xfail(reason="GH-26469")
+    def test_series_constructor_scalar_with_index(self, data, dtype):
+        # TypeError: data type not understood
+        super().test_series_constructor_scalar_with_index(data, dtype)
 
 
 class TestGetitem(BaseDatetimeTests, base.BaseGetitemTests):

pandas/tests/extension/test_numpy.py

@@ -151,6 +151,11 @@ def test_array_from_scalars(self, data):
         # ValueError: PandasArray must be 1-dimensional.
         super().test_array_from_scalars(data)
 
+    @skip_nested
+    def test_series_constructor_scalar_with_index(self, data, dtype):
+        # ValueError: Length of passed values is 1, index implies 3.
+        super().test_series_constructor_scalar_with_index(data, dtype)
+
 
 class TestDtype(BaseNumPyTests, base.BaseDtypeTests):
     @pytest.mark.skip(reason="Incorrect expected.")

pandas/tests/extension/test_sparse.py

@@ -112,7 +112,15 @@ def test_view(self, data):
 
 
 class TestConstructors(BaseSparseTests, base.BaseConstructorsTests):
-    pass
+    @pytest.mark.xfail(reason="GH-26469", strict=False)
+    def test_series_constructor_no_data_with_index(self, dtype, na_value):
+        # ValueError: Cannot convert non-finite values (NA or inf) to integer
+        super().test_series_constructor_no_data_with_index(dtype, na_value)
+
+    @pytest.mark.xfail(reason="GH-26469", strict=False)
+    def test_series_constructor_scalar_na_with_index(self, dtype, na_value):
+        # ValueError: Cannot convert non-finite values (NA or inf) to integer
+        super().test_series_constructor_scalar_na_with_index(dtype, na_value)
 
 
 class TestReshaping(BaseSparseTests, base.BaseReshapingTests):