make _reduce an always defined method on Base; raise TypeError if inv…

…oked and not overriden, test the same

pandas/core/arrays/base.py

@@ -679,6 +679,29 @@ def _ndarray_values(self):
         """
         return np.array(self)
 
+    def _reduce(self, name, skipna=True, **kwargs):
+        """Return a scalar result of performing the op
+
+        Parameters
+        ----------
+        name : str
+            name of the function
+        axis : int, default 0
+            axis over which to apply, defined as 0 currently
+        skipna : bool, default True
+            if True, skip NaN values
+        kwargs : dict
+
+        Returns
+        -------
+        scalar
+
+        Raises
+        ------
+        TypeError : subclass does not define reductions
+        """
+        raise TypeError
+
 
 class ExtensionOpsMixin(object):
     """
@@ -717,25 +740,6 @@ def _add_comparison_ops(cls):
         cls.__le__ = cls._create_comparison_method(operator.le)
         cls.__ge__ = cls._create_comparison_method(operator.ge)
 
-    def _reduce(self, name, skipna=True, **kwargs):
-        """Return a scalar result of performing the op
-
-        Parameters
-        ----------
-        name : str
-            name of the function
-        axis : int, default 0
-            axis over which to apply, defined as 0 currently
-        skipna : bool, default True
-            if True, skip NaN values
-        kwargs : dict
-
-        Returns
-        -------
-        scalar
-        """
-        raise AbstractMethodError(self)
-
 
 class ExtensionScalarOpsMixin(ExtensionOpsMixin):
     """A mixin for defining the arithmetic and logical operations on

pandas/tests/extension/arrow/test_bool.py

@@ -39,6 +39,10 @@ def test_from_dtype(self, data):
         pytest.skip("GH-22666")
 
 
+class TestReduce(base.BaseNoReduceTests):
+    pass
+
+
 def test_is_bool_dtype(data):
     assert pd.api.types.is_bool_dtype(data)
     assert pd.core.common.is_bool_indexer(data)

pandas/tests/extension/base/__init__.py

@@ -48,7 +48,7 @@ class TestMyDtype(BaseDtypeTests):
 from .interface import BaseInterfaceTests  # noqa
 from .methods import BaseMethodsTests  # noqa
 from .ops import BaseArithmeticOpsTests, BaseComparisonOpsTests, BaseOpsUtil  # noqa
-from .reduce import BaseNumericReduceTests, BaseBooleanReduceTests  # noqa
+from .reduce import BaseNoReduceTests, BaseNumericReduceTests, BaseBooleanReduceTests  # noqa
 from .missing import BaseMissingTests  # noqa
 from .reshaping import BaseReshapingTests  # noqa
 from .setitem import BaseSetitemTests  # noqa

pandas/tests/extension/base/reduce.py

@@ -16,6 +16,26 @@ def check_reduce(self, s, op_name, skipna):
         tm.assert_almost_equal(result, expected)
 
 
+class BaseNoReduceTests(BaseReduceTests):
+    """ we don't define any reductions """
+
+    @pytest.mark.parametrize('skipna', [True, False])
+    def test_reduce_series_numeric(self, data, all_numeric_reductions, skipna):
+        op_name = all_numeric_reductions
+        s = pd.Series(data)
+
+        with pytest.raises(TypeError):
+            getattr(s, op_name)(skipna=skipna)
+
+    @pytest.mark.parametrize('skipna', [True, False])
+    def test_reduce_series_boolean(self, data, all_boolean_reductions, skipna):
+        op_name = all_boolean_reductions
+        s = pd.Series(data)
+
+        with pytest.raises(TypeError):
+            getattr(s, op_name)(skipna=skipna)
+
+
 class BaseNumericReduceTests(BaseReduceTests):
 
     @pytest.mark.parametrize('skipna', [True, False])

pandas/tests/extension/decimal/array.py

@@ -136,13 +136,14 @@ def _concat_same_type(cls, to_concat):
 
     def _reduce(self, name, axis=0, skipna=True, **kwargs):
 
-        # select the nan* ops
         if skipna:
-            op = getattr(self.data, 'nan' + name)
+            raise NotImplementedError("decimal does not support skipna=True")
 
-        # don't skip nans
-        else:
+        try:
             op = getattr(self.data, name)
+        except AttributeError:
+            raise NotImplementedError("decimal does not support "
+                                      "the {} operation".format(name))
         return op(axis=axis)
 
 

pandas/tests/extension/decimal/test_decimal.py

@@ -131,6 +131,28 @@ class TestMissing(BaseDecimal, base.BaseMissingTests):
     pass
 
 
+class Reduce:
+
+    def check_reduce(self, s, op_name, skipna):
+
+        if skipna or op_name in ['median']:
+            with pytest.raises(NotImplementedError):
+                getattr(s, op_name)(skipna=skipna)
+
+        else:
+            result = getattr(s, op_name)(skipna=skipna)
+            expected = getattr(np.asarray(s), op_name)()
+            tm.assert_almost_equal(result, expected)
+
+
+class TestNumericReduce(Reduce, base.BaseNumericReduceTests):
+    pass
+
+
+class TestBooleanReduce(Reduce, base.BaseBooleanReduceTests):
+    pass
+
+
 class TestMethods(BaseDecimal, base.BaseMethodsTests):
     @pytest.mark.parametrize('dropna', [True, False])
     @pytest.mark.xfail(reason="value_counts not implemented yet.")

pandas/tests/extension/json/test_json.py

@@ -160,6 +160,10 @@ def test_fillna_frame(self):
                               reason="Dictionary order unstable")
 
 
+class TestReduce(base.BaseNoReduceTests):
+    pass
+
+
 class TestMethods(BaseJSON, base.BaseMethodsTests):
     @unhashable
     def test_value_counts(self, all_data, dropna):

pandas/tests/extension/test_categorical.py

@@ -164,6 +164,10 @@ def test_fillna_limit_backfill(self):
         pass
 
 
+class TestReduce(base.BaseNoReduceTests):
+    pass
+
+
 class TestMethods(base.BaseMethodsTests):
     pass
 

pandas/tests/extension/test_interval.py

@@ -98,6 +98,10 @@ class TestInterface(BaseInterval, base.BaseInterfaceTests):
     pass
 
 
+class TestReduce(base.BaseNoReduceTests):
+    pass
+
+
 class TestMethods(BaseInterval, base.BaseMethodsTests):
 
     @pytest.mark.skip(reason='addition is not defined for intervals')