REF/API: Stricter extension checking.

pandas/core/dtypes/common.py

@@ -9,7 +9,8 @@
 from pandas.core.dtypes.dtypes import (
     registry, CategoricalDtype, CategoricalDtypeType, DatetimeTZDtype,
     DatetimeTZDtypeType, PeriodDtype, PeriodDtypeType, IntervalDtype,
-    IntervalDtypeType, ExtensionDtype)
+    IntervalDtypeType, PandasExtensionDtype, ExtensionDtype,
+    _pandas_registry)
 from pandas.core.dtypes.generic import (
     ABCCategorical, ABCPeriodIndex, ABCDatetimeIndex, ABCSeries,
     ABCSparseArray, ABCSparseSeries, ABCCategoricalIndex, ABCIndexClass,
@@ -1709,17 +1710,9 @@ def is_extension_array_dtype(arr_or_dtype):
     Third-party libraries may implement arrays or types satisfying
     this interface as well.
     """
-    from pandas.core.arrays import ExtensionArray
-
-    if isinstance(arr_or_dtype, (ABCIndexClass, ABCSeries)):
-        arr_or_dtype = arr_or_dtype._values
-
-    try:
-        arr_or_dtype = pandas_dtype(arr_or_dtype)
-    except TypeError:
-        pass
-
-    return isinstance(arr_or_dtype, (ExtensionDtype, ExtensionArray))
+    dtype = getattr(arr_or_dtype, 'dtype', arr_or_dtype)
+    return (isinstance(dtype, ExtensionDtype) or
+            registry.find(dtype) is not None)
 
 
 def is_complex_dtype(arr_or_dtype):
@@ -1999,12 +1992,12 @@ def pandas_dtype(dtype):
         return dtype
 
     # registered extension types
-    result = registry.find(dtype)
+    result = _pandas_registry.find(dtype) or registry.find(dtype)
     if result is not None:
         return result
 
     # un-registered extension types
-    elif isinstance(dtype, ExtensionDtype):
+    elif isinstance(dtype, (PandasExtensionDtype, ExtensionDtype)):
         return dtype
 
     # try a numpy dtype

pandas/core/dtypes/dtypes.py

@@ -22,9 +22,9 @@ class Registry(object):
     --------
     registry.register(MyExtensionDtype)
     """
-    dtypes = []
+    def __init__(self):
+        self.dtypes = []
 
-    @classmethod
     def register(self, dtype):
         """
         Parameters
@@ -50,7 +50,7 @@ def find(self, dtype):
             dtype_type = dtype
             if not isinstance(dtype, type):
                 dtype_type = type(dtype)
-            if issubclass(dtype_type, (PandasExtensionDtype, ExtensionDtype)):
+            if issubclass(dtype_type, ExtensionDtype):
                 return dtype
 
             return None
@@ -65,6 +65,9 @@ def find(self, dtype):
 
 
 registry = Registry()
+# TODO(Extension): remove the second registry once all internal extension
+# dtypes are real extension dtypes.
+_pandas_registry = Registry()
 
 
 class PandasExtensionDtype(_DtypeOpsMixin):
@@ -822,7 +825,7 @@ def is_dtype(cls, dtype):
 
 
 # register the dtypes in search order
-registry.register(DatetimeTZDtype)
-registry.register(PeriodDtype)
 registry.register(IntervalDtype)
 registry.register(CategoricalDtype)
+_pandas_registry.register(DatetimeTZDtype)
+_pandas_registry.register(PeriodDtype)

pandas/tests/dtypes/test_dtypes.py

@@ -9,7 +9,7 @@
 
 from pandas.core.dtypes.dtypes import (
     DatetimeTZDtype, PeriodDtype,
-    IntervalDtype, CategoricalDtype, registry)
+    IntervalDtype, CategoricalDtype, registry, _pandas_registry)
 from pandas.core.dtypes.common import (
     is_categorical_dtype, is_categorical,
     is_datetime64tz_dtype, is_datetimetz,
@@ -775,21 +775,31 @@ def test_update_dtype_errors(self, bad_dtype):
 
 @pytest.mark.parametrize(
     'dtype',
-    [DatetimeTZDtype, CategoricalDtype,
-     PeriodDtype, IntervalDtype])
+    [CategoricalDtype, IntervalDtype])
 def test_registry(dtype):
     assert dtype in registry.dtypes
 
 
+@pytest.mark.parametrize('dtype', [DatetimeTZDtype, PeriodDtype])
+def test_pandas_registry(dtype):
+    assert dtype not in registry.dtypes
+    assert dtype in _pandas_registry.dtypes
+
+
 @pytest.mark.parametrize(
     'dtype, expected',
     [('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'))])
+     ('category', CategoricalDtype())])
 def test_registry_find(dtype, expected):
-
     assert registry.find(dtype) == expected
+
+
+@pytest.mark.parametrize(
+    'dtype, expected',
+    [('period[D]', PeriodDtype('D')),
+     ('datetime64[ns, US/Eastern]', DatetimeTZDtype('ns', 'US/Eastern'))])
+def test_pandas_registry_find(dtype, expected):
+    assert _pandas_registry.find(dtype) == expected