Backport PR #54496 on branch 2.1.x (Fix inference for fixed with numpy strings with arrow string option) (#54672)

Backport PR #54496: Fix inference for fixed with numpy strings with arrow string option

Co-authored-by: Patrick Hoefler <61934744+phofl@users.noreply.github.com>

Author: meeseeksmachine

pandas/core/construction.py

@@ -19,6 +19,8 @@
 import numpy as np
 from numpy import ma
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas._libs import lib
 from pandas._libs.tslibs import (
     Period,
@@ -49,7 +51,10 @@
     is_object_dtype,
     pandas_dtype,
 )
-from pandas.core.dtypes.dtypes import NumpyEADtype
+from pandas.core.dtypes.dtypes import (
+    ArrowDtype,
+    NumpyEADtype,
+)
 from pandas.core.dtypes.generic import (
     ABCDataFrame,
     ABCExtensionArray,
@@ -589,6 +594,11 @@ def sanitize_array(
             subarr = data
             if data.dtype == object:
                 subarr = maybe_infer_to_datetimelike(data)
+            elif data.dtype.kind == "U" and using_pyarrow_string_dtype():
+                import pyarrow as pa
+
+                dtype = ArrowDtype(pa.string())
+                subarr = dtype.construct_array_type()._from_sequence(data, dtype=dtype)
 
             if subarr is data and copy:
                 subarr = subarr.copy()

pandas/core/internals/construction.py

@@ -13,6 +13,8 @@
 import numpy as np
 from numpy import ma
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas._libs import lib
 
 from pandas.core.dtypes.astype import astype_is_view
@@ -30,7 +32,10 @@
     is_named_tuple,
     is_object_dtype,
 )
-from pandas.core.dtypes.dtypes import ExtensionDtype
+from pandas.core.dtypes.dtypes import (
+    ArrowDtype,
+    ExtensionDtype,
+)
 from pandas.core.dtypes.generic import (
     ABCDataFrame,
     ABCSeries,
@@ -65,6 +70,7 @@
 from pandas.core.internals.blocks import (
     BlockPlacement,
     ensure_block_shape,
+    new_block,
     new_block_2d,
 )
 from pandas.core.internals.managers import (
@@ -372,6 +378,20 @@ def ndarray_to_mgr(
             bp = BlockPlacement(slice(len(columns)))
             nb = new_block_2d(values, placement=bp, refs=refs)
             block_values = [nb]
+    elif dtype is None and values.dtype.kind == "U" and using_pyarrow_string_dtype():
+        import pyarrow as pa
+
+        obj_columns = list(values)
+        dtype = ArrowDtype(pa.string())
+        block_values = [
+            new_block(
+                dtype.construct_array_type()._from_sequence(data, dtype=dtype),
+                BlockPlacement(slice(i, i + 1)),
+                ndim=1,
+            )
+            for i, data in enumerate(obj_columns)
+        ]
+
     else:
         bp = BlockPlacement(slice(len(columns)))
         nb = new_block_2d(values, placement=bp, refs=refs)

pandas/tests/frame/test_constructors.py

@@ -2718,6 +2718,31 @@ def test_frame_string_inference(self):
             df = DataFrame({"a": ["a", "b"]}, dtype="object")
         tm.assert_frame_equal(df, expected)
 
+    def test_frame_string_inference_array_string_dtype(self):
+        # GH#54496
+        pa = pytest.importorskip("pyarrow")
+        dtype = pd.ArrowDtype(pa.string())
+        expected = DataFrame(
+            {"a": ["a", "b"]}, dtype=dtype, columns=Index(["a"], dtype=dtype)
+        )
+        with pd.option_context("future.infer_string", True):
+            df = DataFrame({"a": np.array(["a", "b"])})
+        tm.assert_frame_equal(df, expected)
+
+        expected = DataFrame({0: ["a", "b"], 1: ["c", "d"]}, dtype=dtype)
+        with pd.option_context("future.infer_string", True):
+            df = DataFrame(np.array([["a", "c"], ["b", "d"]]))
+        tm.assert_frame_equal(df, expected)
+
+        expected = DataFrame(
+            {"a": ["a", "b"], "b": ["c", "d"]},
+            dtype=dtype,
+            columns=Index(["a", "b"], dtype=dtype),
+        )
+        with pd.option_context("future.infer_string", True):
+            df = DataFrame(np.array([["a", "c"], ["b", "d"]]), columns=["a", "b"])
+        tm.assert_frame_equal(df, expected)
+
 
 class TestDataFrameConstructorIndexInference:
     def test_frame_from_dict_of_series_overlapping_monthly_period_indexes(self):

pandas/tests/series/test_constructors.py

@@ -2107,6 +2107,14 @@ def test_series_string_inference_scalar(self):
             ser = Series("a", index=[1])
         tm.assert_series_equal(ser, expected)
 
+    def test_series_string_inference_array_string_dtype(self):
+        # GH#54496
+        pa = pytest.importorskip("pyarrow")
+        expected = Series(["a", "b"], dtype=pd.ArrowDtype(pa.string()))
+        with pd.option_context("future.infer_string", True):
+            ser = Series(np.array(["a", "b"]))
+        tm.assert_series_equal(ser, expected)
+
 
 class TestSeriesConstructorIndexCoercion:
     def test_series_constructor_datetimelike_index_coercion(self):