ENH: EA.tolist (#43920)

Author: jbrockmendel

doc/source/reference/extensions.rst

@@ -60,6 +60,7 @@ objects.
       api.extensions.ExtensionArray.nbytes
       api.extensions.ExtensionArray.ndim
       api.extensions.ExtensionArray.shape
+      api.extensions.ExtensionArray.tolist
 
 Additionally, we have some utility methods for ensuring your object
 behaves correctly.

pandas/core/arrays/base.py

@@ -130,6 +130,7 @@ class ExtensionArray:
     searchsorted
     shift
     take
+    tolist
     unique
     view
     _concat_same_type
@@ -1348,6 +1349,22 @@ def _reduce(self, name: str, *, skipna: bool = True, **kwargs):
     # ------------------------------------------------------------------------
     # Non-Optimized Default Methods
 
+    def tolist(self) -> list:
+        """
+        Return a list of the values.
+
+        These are each a scalar type, which is a Python scalar
+        (for str, int, float) or a pandas scalar
+        (for Timestamp/Timedelta/Interval/Period)
+
+        Returns
+        -------
+        list
+        """
+        if self.ndim > 1:
+            return [x.tolist() for x in self]
+        return list(self)
+
     def delete(self: ExtensionArrayT, loc: PositionalIndexer) -> ExtensionArrayT:
         indexer = np.delete(np.arange(len(self)), loc)
         return self.take(indexer)

pandas/core/arrays/categorical.py

@@ -40,7 +40,6 @@
     Ordered,
     PositionalIndexer2D,
     PositionalIndexerTuple,
-    Scalar,
     ScalarIndexer,
     SequenceIndexer,
     Shape,
@@ -566,17 +565,11 @@ def itemsize(self) -> int:
         """
         return self.categories.itemsize
 
-    def tolist(self) -> list[Scalar]:
+    def to_list(self):
         """
-        Return a list of the values.
-
-        These are each a scalar type, which is a Python scalar
-        (for str, int, float) or a pandas scalar
-        (for Timestamp/Timedelta/Interval/Period)
+        Alias for tolist.
         """
-        return list(self)
-
-    to_list = tolist
+        return self.tolist()
 
     @classmethod
     def _from_inferred_categories(

pandas/core/base.py

@@ -740,9 +740,6 @@ def tolist(self):
         numpy.ndarray.tolist : Return the array as an a.ndim-levels deep
             nested list of Python scalars.
         """
-        if not isinstance(self._values, np.ndarray):
-            # check for ndarray instead of dtype to catch DTA/TDA
-            return list(self._values)
         return self._values.tolist()
 
     to_list = tolist

pandas/tests/extension/base/dim2.py

@@ -97,6 +97,17 @@ def test_iter_2d(self, data):
             assert obj.ndim == 1
             assert len(obj) == arr2d.shape[1]
 
+    def test_tolist_2d(self, data):
+        arr2d = data.reshape(1, -1)
+
+        result = arr2d.tolist()
+        expected = [data.tolist()]
+
+        assert isinstance(result, list)
+        assert all(isinstance(x, list) for x in result)
+
+        assert result == expected
+
     def test_concat_2d(self, data):
         left = data.reshape(-1, 1)
         right = left.copy()

pandas/tests/extension/base/interface.py

@@ -119,3 +119,9 @@ def test_view(self, data):
 
         # check specifically that the `dtype` kwarg is accepted
         data.view(dtype=None)
+
+    def test_tolist(self, data):
+        result = data.tolist()
+        expected = list(data)
+        assert isinstance(result, list)
+        assert result == expected