BUG: Redefine IndexOpsMixin.size, fix #25580.

doc/source/whatsnew/v0.24.2.rst

@@ -31,6 +31,7 @@ Fixed Regressions
 - Fixed regression in ``IntervalDtype`` construction where passing an incorrect string with 'Interval' as a prefix could result in a ``RecursionError``. (:issue:`25338`)
 - Fixed regression in :class:`Categorical`, where constructing it from a categorical ``Series`` and an explicit ``categories=`` that differed from that in the ``Series`` created an invalid object which could trigger segfaults. (:issue:`25318`)
 - Fixed pip installing from source into an environment without NumPy (:issue:`25193`)
+- Fixed bug where :meth:`Index.size` could not return correct result for :class:`api.extensions.ExtensionArray` (:issue:`25580`)
 
 .. _whatsnew_0242.enhancements:
 

pandas/core/base.py

@@ -762,7 +762,7 @@ def size(self):
         """
         Return the number of elements in the underlying data.
         """
-        return self._values.size
+        return len(self._values)
 
     @property
     def flags(self):

pandas/tests/resample/test_datetime_index.py

@@ -101,6 +101,18 @@ def test_resample_basic(series, closed, expected):
     assert_series_equal(result, expected)
 
 
+def test_resample_integerarray():
+    # GH 25580, resample on IntegerArray
+    ts = pd.Series(range(9),
+                   index=pd.date_range('1/1/2000', periods=9, freq='T'),
+                   dtype='Int64')
+    result = ts.resample('3T').sum()
+    expected = Series([3, 12, 21],
+                      index=pd.date_range('1/1/2000', periods=3, freq='3T'),
+                      dtype="Int64")
+    assert_series_equal(result, expected)
+
+
 def test_resample_basic_grouper(series):
     s = series
     result = s.resample('5Min').last()

pandas/tests/series/test_api.py

@@ -493,6 +493,13 @@ def test_tab_complete_warning(self, ip):
             with provisionalcompleter('ignore'):
                 list(ip.Completer.completions('s.', 1))
 
+    def test_integer_series_size(self):
+        # GH 25580
+        s = Series(range(9))
+        assert s.size == 9
+        s = Series(range(9), dtype="Int64")
+        assert s.size == 9
+
 
 class TestCategoricalSeries(object):