Support dtype_backend="pandas|pyarrow" configuration

dask/dask-schema.yaml

@@ -72,6 +72,14 @@ properties:
               task when reading a parquet dataset from a REMOTE file system.
               Specifying 0 will result in serial execution on the client.
 
+      nullable_backend:
+        enum:
+          - pandas
+          - pyarrow
+        description: |
+          The nullable dtype implementation to use. Must be either "pandas" or
+          "pyarrow". Default is "pandas".
+
   array:
     type: object
     properties:

dask/dask.yaml

@@ -12,6 +12,7 @@ dataframe:
   parquet:
     metadata-task-size-local: 512  # Number of files per local metadata-processing task
     metadata-task-size-remote: 16  # Number of files per remote metadata-processing task
+  nullable_backend: "pandas"  # Nullable dtype implementation to use
 
 array:
   backend: "numpy"  # Backend array library for input IO and data creation

dask/dataframe/io/parquet/arrow.py

@@ -1580,19 +1580,31 @@ def _arrow_table_to_pandas(
         _kwargs.update({"use_threads": False, "ignore_metadata": False})
 
         if use_nullable_dtypes:
+            # Determine is `pandas` or `pyarrow`-backed dtypes should be used
+            if use_nullable_dtypes == "pandas":
+                default_types_mapper = PYARROW_NULLABLE_DTYPE_MAPPING.get
+            else:
+                # use_nullable_dtypes == "pyarrow"
+
+                def default_types_mapper(pyarrow_dtype):  # type: ignore
+                    # Special case pyarrow strings to use more feature complete dtype
+                    # See https://github.com/pandas-dev/pandas/issues/50074
+                    if pyarrow_dtype == pa.string():
+                        return pd.StringDtype("pyarrow")
+                    else:
+                        return pd.ArrowDtype(pyarrow_dtype)
+
             if "types_mapper" in _kwargs:
-                # User-provided entries take priority over PYARROW_NULLABLE_DTYPE_MAPPING
+                # User-provided entries take priority over default_types_mapper
                 types_mapper = _kwargs["types_mapper"]
 
                 def _types_mapper(pa_type):
-                    return types_mapper(pa_type) or PYARROW_NULLABLE_DTYPE_MAPPING.get(
-                        pa_type
-                    )
+                    return types_mapper(pa_type) or default_types_mapper(pa_type)
 
                 _kwargs["types_mapper"] = _types_mapper
 
             else:
-                _kwargs["types_mapper"] = PYARROW_NULLABLE_DTYPE_MAPPING.get
+                _kwargs["types_mapper"] = default_types_mapper
 
         return arrow_table.to_pandas(categories=categories, **_kwargs)
 

dask/dataframe/io/parquet/core.py

@@ -185,7 +185,7 @@ def read_parquet(
     index=None,
     storage_options=None,
     engine="auto",
-    use_nullable_dtypes=False,
+    use_nullable_dtypes: bool = False,
     calculate_divisions=None,
     ignore_metadata_file=False,
     metadata_task_size=None,
@@ -257,6 +257,22 @@ def read_parquet(
     engine : {'auto', 'pyarrow', 'fastparquet'}, default 'auto'
         Parquet library to use. Defaults to 'auto', which uses ``pyarrow`` if
         it is installed, and falls back to ``fastparquet`` otherwise.
+    use_nullable_dtypes : {False, True}
+        Whether to use extension dtypes for the resulting ``DataFrame``.
+        ``use_nullable_dtypes=True`` is only supported when ``engine="pyarrow"``.
+
+        .. note::
+
+            Use the ``dataframe.nullable_backend`` config option to select which
+            dtype implementation to use.
+
+            ``dataframe.nullable_backend="pandas"`` (the default) will use
+            pandas' ``numpy``-backed nullable dtypes (e.g. ``Int64``,
+            ``string[python]``, etc.) while ``dataframe.nullable_backend="pyarrow"``
+            will use ``pyarrow``-backed extension dtypes (e.g. ``int64[pyarrow]``,
+            ``string[pyarrow]``, etc.). ``dataframe.nullable_backend="pyarrow"``
+            requires ``pandas`` 1.5+.
+
     calculate_divisions : bool, default False
         Whether to use min/max statistics from the footer metadata (or global
         ``_metadata`` file) to calculate divisions for the output DataFrame
@@ -366,6 +382,9 @@ def read_parquet(
     pyarrow.parquet.ParquetDataset
     """
 
+    if use_nullable_dtypes:
+        use_nullable_dtypes = dask.config.get("dataframe.nullable_backend")
+
     # "Pre-deprecation" warning for `chunksize`
     if chunksize:
         warnings.warn(
@@ -552,7 +571,7 @@ def read_parquet(
     if "retries" not in annotations and not _is_local_fs(fs):
         ctx = dask.annotate(retries=5)
     else:
-        ctx = contextlib.nullcontext()
+        ctx = contextlib.nullcontext()  # type: ignore
 
     with ctx:
         # Construct the output collection with from_map

dask/dataframe/io/tests/test_parquet.py

@@ -15,7 +15,12 @@
 import dask.dataframe as dd
 import dask.multiprocessing
 from dask.blockwise import Blockwise, optimize_blockwise
-from dask.dataframe._compat import PANDAS_GT_110, PANDAS_GT_121, PANDAS_GT_130
+from dask.dataframe._compat import (
+    PANDAS_GT_110,
+    PANDAS_GT_121,
+    PANDAS_GT_130,
+    PANDAS_GT_150,
+)
 from dask.dataframe.io.parquet.core import get_engine
 from dask.dataframe.io.parquet.utils import _parse_pandas_metadata
 from dask.dataframe.optimize import optimize_dataframe_getitem
@@ -618,17 +623,37 @@ def test_roundtrip_nullable_dtypes(tmp_path, write_engine, read_engine):
 
 
 @PYARROW_MARK
-def test_use_nullable_dtypes(tmp_path, engine):
+@pytest.mark.parametrize(
+    "nullable_backend",
+    [
+        "pandas",
+        pytest.param(
+            "pyarrow",
+            marks=pytest.mark.skipif(
+                not PANDAS_GT_150, reason="Requires pyarrow-backed nullable dtypes"
+            ),
+        ),
+    ],
+)
+def test_use_nullable_dtypes(tmp_path, engine, nullable_backend):
     """
     Test reading a parquet file without pandas metadata,
     but forcing use of nullable dtypes where appropriate
     """
+
+    if nullable_backend == "pandas":
+        dtype_extra = ""
+    else:
+        # nullable_backend == "pyarrow"
+        dtype_extra = "[pyarrow]"
     df = pd.DataFrame(
         {
-            "a": pd.Series([1, 2, pd.NA, 3, 4], dtype="Int64"),
-            "b": pd.Series([True, pd.NA, False, True, False], dtype="boolean"),
-            "c": pd.Series([0.1, 0.2, 0.3, pd.NA, 0.4], dtype="Float64"),
-            "d": pd.Series(["a", "b", "c", "d", pd.NA], dtype="string"),
+            "a": pd.Series([1, 2, pd.NA, 3, 4], dtype=f"Int64{dtype_extra}"),
+            "b": pd.Series(
+                [True, pd.NA, False, True, False], dtype=f"boolean{dtype_extra}"
+            ),
+            "c": pd.Series([0.1, 0.2, 0.3, pd.NA, 0.4], dtype=f"Float64{dtype_extra}"),
+            "d": pd.Series(["a", "b", "c", "d", pd.NA], dtype=f"string{dtype_extra}"),
         }
     )
     ddf = dd.from_pandas(df, npartitions=2)
@@ -644,21 +669,24 @@ def write_partition(df, i):
     partitions = ddf.to_delayed()
     dask.compute([write_partition(p, i) for i, p in enumerate(partitions)])
 
-    # Not supported by fastparquet
-    if engine == "fastparquet":
-        with pytest.raises(ValueError, match="`use_nullable_dtypes` is not supported"):
-            dd.read_parquet(tmp_path, engine=engine, use_nullable_dtypes=True)
+    with dask.config.set({"dataframe.nullable_backend": nullable_backend}):
+        # Not supported by fastparquet
+        if engine == "fastparquet":
+            with pytest.raises(
+                ValueError, match="`use_nullable_dtypes` is not supported"
+            ):
+                dd.read_parquet(tmp_path, engine=engine, use_nullable_dtypes=True)
 
-    # Works in pyarrow
-    else:
-        # Doesn't round-trip by default when we aren't using nullable dtypes
-        with pytest.raises(AssertionError):
-            ddf2 = dd.read_parquet(tmp_path, engine=engine)
-            assert_eq(df, ddf2)
-
-        # Round trip works when we use nullable dtypes
-        ddf2 = dd.read_parquet(tmp_path, engine=engine, use_nullable_dtypes=True)
-        assert_eq(df, ddf2, check_index=False)
+        # Works in pyarrow
+        else:
+            # Doesn't round-trip by default when we aren't using nullable dtypes
+            with pytest.raises(AssertionError):
+                ddf2 = dd.read_parquet(tmp_path, engine=engine)
+                assert_eq(df, ddf2)
+
+            # Round trip works when we use nullable dtypes
+            ddf2 = dd.read_parquet(tmp_path, engine=engine, use_nullable_dtypes=True)
+            assert_eq(df, ddf2, check_index=False)
 
 
 @pytest.mark.xfail(

dask/tests/test_spark_compat.py

@@ -1,19 +1,22 @@
+import decimal
 import signal
 import sys
 import threading
 
 import pytest
 
+import dask
 from dask.datasets import timeseries
 
 dd = pytest.importorskip("dask.dataframe")
 pyspark = pytest.importorskip("pyspark")
-pytest.importorskip("pyarrow")
+pa = pytest.importorskip("pyarrow")
 pytest.importorskip("fastparquet")
 
 import numpy as np
 import pandas as pd
 
+from dask.dataframe._compat import PANDAS_GT_150
 from dask.dataframe.utils import assert_eq
 
 pytestmark = pytest.mark.skipif(
@@ -149,3 +152,43 @@ def test_roundtrip_parquet_spark_to_dask_extension_dtypes(spark_session, tmpdir)
         [pd.api.types.is_extension_array_dtype(dtype) for dtype in ddf.dtypes]
     ), ddf.dtypes
     assert_eq(ddf, pdf, check_index=False)
+
+
+@pytest.mark.skipif(not PANDAS_GT_150, reason="Requires pyarrow-backed nullable dtypes")
+def test_read_decimal_dtype_pyarrow(spark_session, tmpdir):
+    tmpdir = str(tmpdir)
+    npartitions = 3
+    size = 6
+
+    decimal_data = [
+        decimal.Decimal("8093.234"),
+        decimal.Decimal("8094.234"),
+        decimal.Decimal("8095.234"),
+        decimal.Decimal("8096.234"),
+        decimal.Decimal("8097.234"),
+        decimal.Decimal("8098.234"),
+    ]
+    pdf = pd.DataFrame(
+        {
+            "a": range(size),
+            "b": decimal_data,
+        }
+    )
+    sdf = spark_session.createDataFrame(pdf)
+    sdf = sdf.withColumn("b", sdf["b"].cast(pyspark.sql.types.DecimalType(7, 3)))
+    # We are not overwriting any data, but spark complains if the directory
+    # already exists (as tmpdir does) and we don't set overwrite
+    sdf.repartition(npartitions).write.parquet(tmpdir, mode="overwrite")
+
+    with dask.config.set({"dataframe.nullable_backend": "pyarrow"}):
+        ddf = dd.read_parquet(tmpdir, engine="pyarrow", use_nullable_dtypes=True)
+    assert ddf.b.dtype.pyarrow_dtype == pa.decimal128(7, 3)
+    assert ddf.b.compute().dtype.pyarrow_dtype == pa.decimal128(7, 3)
+    expected = pdf.astype(
+        {
+            "a": "int64[pyarrow]",
+            "b": pd.ArrowDtype(pa.decimal128(7, 3)),
+        }
+    )
+
+    assert_eq(ddf, expected, check_index=False)