BUG: Ensure .astype doesn't use PandasArray (pandas-dev#24866)

Author: TomAugspurger

pandas/core/internals/blocks.py

@@ -27,13 +27,13 @@
     CategoricalDtype, ExtensionDtype, PandasExtensionDtype)
 from pandas.core.dtypes.generic import (
     ABCDataFrame, ABCDatetimeIndex, ABCExtensionArray, ABCIndexClass,
-    ABCSeries)
+    ABCPandasArray, ABCSeries)
 from pandas.core.dtypes.missing import (
     _isna_compat, array_equivalent, isna, notna)
 
 import pandas.core.algorithms as algos
 from pandas.core.arrays import (
-    Categorical, DatetimeArray, ExtensionArray, TimedeltaArray)
+    Categorical, DatetimeArray, ExtensionArray, PandasDtype, TimedeltaArray)
 from pandas.core.base import PandasObject
 import pandas.core.common as com
 from pandas.core.indexes.datetimes import DatetimeIndex
@@ -576,23 +576,14 @@ def _astype(self, dtype, copy=False, errors='raise', values=None,
 
             return self.make_block(Categorical(self.values, dtype=dtype))
 
-        # convert dtypes if needed
         dtype = pandas_dtype(dtype)
+
         # astype processing
         if is_dtype_equal(self.dtype, dtype):
             if copy:
                 return self.copy()
             return self
 
-        klass = None
-        if is_sparse(self.values):
-            # special case sparse, Series[Sparse].astype(object) is sparse
-            klass = ExtensionBlock
-        elif is_object_dtype(dtype):
-            klass = ObjectBlock
-        elif is_extension_array_dtype(dtype):
-            klass = ExtensionBlock
-
         try:
             # force the copy here
             if values is None:
@@ -624,7 +615,7 @@ def _astype(self, dtype, copy=False, errors='raise', values=None,
                     pass
 
             newb = make_block(values, placement=self.mgr_locs,
-                              klass=klass, ndim=self.ndim)
+                              ndim=self.ndim)
         except Exception:  # noqa: E722
             if errors == 'raise':
                 raise
@@ -3041,6 +3032,13 @@ def get_block_type(values, dtype=None):
 
 def make_block(values, placement, klass=None, ndim=None, dtype=None,
                fastpath=None):
+    # Ensure that we don't allow PandasArray / PandasDtype in internals.
+    # For now, blocks should be backed by ndarrays when possible.
+    if isinstance(values, ABCPandasArray):
+        values = values.to_numpy()
+    if isinstance(dtype, PandasDtype):
+        dtype = dtype.numpy_dtype
+
     if fastpath is not None:
         # GH#19265 pyarrow is passing this
         warnings.warn("fastpath argument is deprecated, will be removed "

pandas/tests/internals/test_internals.py

@@ -1291,3 +1291,23 @@ def test_block_shape():
 
     assert (a._data.blocks[0].mgr_locs.indexer ==
             b._data.blocks[0].mgr_locs.indexer)
+
+
+def test_make_block_no_pandas_array():
+    # https://github.com/pandas-dev/pandas/pull/24866
+    arr = pd.array([1, 2])
+
+    # PandasArray, no dtype
+    result = make_block(arr, slice(len(arr)))
+    assert result.is_integer is True
+    assert result.is_extension is False
+
+    # PandasArray, PandasDtype
+    result = make_block(arr, slice(len(arr)), dtype=arr.dtype)
+    assert result.is_integer is True
+    assert result.is_extension is False
+
+    # ndarray, PandasDtype
+    result = make_block(arr.to_numpy(), slice(len(arr)), dtype=arr.dtype)
+    assert result.is_integer is True
+    assert result.is_extension is False

pandas/tests/series/test_internals.py

@@ -312,6 +312,14 @@ def test_constructor_no_pandas_array(self):
         tm.assert_series_equal(ser, result)
         assert isinstance(result._data.blocks[0], IntBlock)
 
+    def test_astype_no_pandas_dtype(self):
+        # https://github.com/pandas-dev/pandas/pull/24866
+        ser = pd.Series([1, 2], dtype="int64")
+        # Don't have PandasDtype in the public API, so we use `.array.dtype`,
+        # which is a PandasDtype.
+        result = ser.astype(ser.array.dtype)
+        tm.assert_series_equal(result, ser)
+
     def test_from_array(self):
         result = pd.Series(pd.array(['1H', '2H'], dtype='timedelta64[ns]'))
         assert result._data.blocks[0].is_extension is False