review comments

Author: jreback

doc/source/whatsnew/v0.24.0.txt

@@ -128,6 +128,9 @@ ExtensionType Changes
 - ``ExtensionDtype`` has gained the ability to instantiate from string dtypes, e.g. ``decimal`` would instantiate a registered ``DecimalDtype``; furthermore
   the dtype has gained the ``construct_array_type`` (:issue:`21185`)
 - The ``ExtensionArray`` constructor, ``_from_sequence`` now take the keyword arg ``copy=False`` (:issue:`21185`)
+- :meth:`Series.combine()` works correctly with :class:`~pandas.api.extensions.ExtensionArray` inside of :class:`Series` (:issue:`20825`)
+- :meth:`Series.combine()` with scalar argument now works for any function type (:issue:`21248`)
+-
 
 .. _whatsnew_0240.api.other:
 
@@ -324,12 +327,6 @@ Reshaping
 -
 -
 
-ExtensionArray
-^^^^^^^^^^^^^^
-
-- :meth:`Series.combine()` works correctly with :class:`~pandas.api.extensions.ExtensionArray` inside of :class:`Series` (:issue:`20825`)
-- :meth:`Series.combine()` with scalar argument now works for any function type (:issue:`21248`)
--
 -
 
 Other

pandas/core/arrays/base.py

@@ -92,7 +92,7 @@ def _from_sequence(cls, scalars, copy=False):
         scalars : Sequence
             Each element will be an instance of the scalar type for this
             array, ``cls.dtype.type``.
-        copy : boolean, default True
+        copy : boolean, default False
             if True, copy the underlying data
         Returns
         -------

pandas/core/dtypes/base.py

@@ -173,8 +173,6 @@ def construct_array_type(cls, array=None):
         -------
         type
         """
-        if array is None:
-            return cls
         raise NotImplementedError
 
     @classmethod

pandas/core/dtypes/dtypes.py

@@ -9,13 +9,14 @@
 
 
 class Registry(object):
-    """ Registry for dtype inference
+    """
+    Registry for dtype inference
 
-    We can directly construct dtypes in pandas_dtypes if they are
-    a type; the registry allows us to register an extension dtype
-    to try inference from a string or a dtype class
+    The registry allows one to map a string repr of a extension
+    dtype to an extenstion dtype.
 
-    These are tried in order for inference.
+    Multiple extension types can be registered.
+    These are tried in order.
 
     Examples
     --------

pandas/tests/dtypes/test_dtypes.py

@@ -788,6 +788,7 @@ def test_registry(dtype):
     [('int64', None),
      ('interval', IntervalDtype()),
      ('interval[int64]', IntervalDtype()),
+     ('interval[datetime64[ns]]', IntervalDtype('datetime64[ns]')),
      ('category', CategoricalDtype()),
      ('period[D]', PeriodDtype('D')),
      ('datetime64[ns, US/Eastern]', DatetimeTZDtype('ns', 'US/Eastern'))])

pandas/tests/extension/base/constructors.py

@@ -52,8 +52,8 @@ def test_from_dtype(self, data):
         dtype = data.dtype
 
         expected = pd.Series(data)
-        result = pd.Series(np.array(data), dtype=dtype)
+        result = pd.Series(list(data), dtype=dtype)
         self.assert_series_equal(result, expected)
 
-        result = pd.Series(np.array(data), dtype=str(dtype))
+        result = pd.Series(list(data), dtype=str(dtype))
         self.assert_series_equal(result, expected)