Add pylibcudf.Scalar.from_py for construction from Python strings, …

…bool, int, float (#17898)

Towards #17054

Authors:
  - Matthew Roeschke (https://github.com/mroeschke)
  - Vyas Ramasubramani (https://github.com/vyasr)

Approvers:
  - Matthew Murray (https://github.com/Matt711)
  - Vyas Ramasubramani (https://github.com/vyasr)

URL: #17898

python/pylibcudf/pylibcudf/libcudf/scalar/scalar_factories.pxd

@@ -1,7 +1,8 @@
-# Copyright (c) 2024, NVIDIA CORPORATION.
+# Copyright (c) 2024-2025, NVIDIA CORPORATION.
 from libcpp.memory cimport unique_ptr
 from libcpp.string cimport string
 from pylibcudf.exception_handler cimport libcudf_exception_handler
+from pylibcudf.libcudf.types cimport data_type
 from pylibcudf.libcudf.column.column_view cimport column_view
 from pylibcudf.libcudf.scalar.scalar cimport scalar
 
@@ -13,7 +14,9 @@ cdef extern from "cudf/scalar/scalar_factories.hpp" namespace "cudf" nogil:
     cdef unique_ptr[scalar] make_fixed_width_scalar[T](
         T value
     ) except +libcudf_exception_handler
-
+    cdef unique_ptr[scalar] make_numeric_scalar(
+        data_type type_
+    ) except +libcudf_exception_handler
     cdef unique_ptr[scalar] make_empty_scalar_like(
         const column_view &
     ) except +libcudf_exception_handler

python/pylibcudf/pylibcudf/scalar.pyx

@@ -1,16 +1,30 @@
-# Copyright (c) 2023-2024, NVIDIA CORPORATION.
+# Copyright (c) 2023-2025, NVIDIA CORPORATION.
 
+from cpython cimport bool as py_bool, datetime
 from cython cimport no_gc_clear
+from libc.stdint cimport int64_t
+from libcpp cimport bool as cbool
 from libcpp.memory cimport unique_ptr
 from libcpp.utility cimport move
-from pylibcudf.libcudf.scalar.scalar cimport scalar
-from pylibcudf.libcudf.scalar.scalar_factories cimport make_empty_scalar_like
+from pylibcudf.libcudf.scalar.scalar cimport (
+    scalar,
+    numeric_scalar,
+)
+from pylibcudf.libcudf.scalar.scalar_factories cimport (
+    make_empty_scalar_like,
+    make_string_scalar,
+    make_numeric_scalar,
+)
+from pylibcudf.libcudf.types cimport type_id
+
 
 from rmm.pylibrmm.memory_resource cimport get_current_device_resource
 
 from .column cimport Column
 from .types cimport DataType
 
+from functools import singledispatch
+
 __all__ = ["Scalar"]
 
 
@@ -79,3 +93,76 @@ cdef class Scalar:
         s.c_obj.swap(libcudf_scalar)
         s._data_type = DataType.from_libcudf(s.get().type())
         return s
+
+    @classmethod
+    def from_py(cls, py_val):
+        """
+        Convert a Python standard library object to a Scalar.
+
+        Parameters
+        ----------
+        py_val: bool, int, float, str, datetime.datetime, datetime.timedelta, list, dict
+            Value to convert to a pylibcudf.Scalar
+
+        Returns
+        -------
+        Scalar
+            New pylibcudf.Scalar
+        """
+        return _from_py(py_val)
+
+cdef Scalar _new_scalar(unique_ptr[scalar] c_obj, DataType dtype):
+    cdef Scalar s = Scalar.__new__(Scalar)
+    s.c_obj.swap(c_obj)
+    s._data_type = dtype
+    return s
+
+
+@singledispatch
+def _from_py(py_val):
+    raise TypeError(f"{type(py_val).__name__} cannot be converted to pylibcudf.Scalar")
+
+
+@_from_py.register(dict)
+@_from_py.register(list)
+@_from_py.register(datetime.datetime)
+@_from_py.register(datetime.timedelta)
+def _(py_val):
+    raise NotImplementedError(
+        f"Conversion from {type(py_val).__name__} is currently not supported."
+    )
+
+
+@_from_py.register(float)
+def _(py_val):
+    cdef DataType dtype = DataType(type_id.FLOAT64)
+    cdef unique_ptr[scalar] c_obj = make_numeric_scalar(dtype.c_obj)
+    (<numeric_scalar[double]*>c_obj.get()).set_value(py_val)
+    cdef Scalar slr = _new_scalar(move(c_obj), dtype)
+    return slr
+
+
+@_from_py.register(int)
+def _(py_val):
+    cdef DataType dtype = DataType(type_id.INT64)
+    cdef unique_ptr[scalar] c_obj = make_numeric_scalar(dtype.c_obj)
+    (<numeric_scalar[int64_t]*>c_obj.get()).set_value(py_val)
+    cdef Scalar slr = _new_scalar(move(c_obj), dtype)
+    return slr
+
+
+@_from_py.register(py_bool)
+def _(py_val):
+    cdef DataType dtype = DataType(type_id.BOOL8)
+    cdef unique_ptr[scalar] c_obj = make_numeric_scalar(dtype.c_obj)
+    (<numeric_scalar[cbool]*>c_obj.get()).set_value(py_val)
+    cdef Scalar slr = _new_scalar(move(c_obj), dtype)
+    return slr
+
+
+@_from_py.register(str)
+def _(py_val):
+    cdef DataType dtype = DataType(type_id.STRING)
+    cdef unique_ptr[scalar] c_obj = make_string_scalar(py_val.encode())
+    cdef Scalar slr = _new_scalar(move(c_obj), dtype)
+    return slr

python/pylibcudf/pylibcudf/tests/test_scalar.py

@@ -0,0 +1,30 @@
+# Copyright (c) 2024-2025, NVIDIA CORPORATION.
+import datetime
+
+import pyarrow as pa
+import pytest
+
+import pylibcudf as plc
+
+
+@pytest.mark.parametrize(
+    "val", [True, False, -1, 0, 1 - 1.0, 0.0, 1.52, "", "a1!"]
+)
+def test_from_py(val):
+    result = plc.Scalar.from_py(val)
+    expected = pa.scalar(val)
+    assert plc.interop.to_arrow(result).equals(expected)
+
+
+@pytest.mark.parametrize(
+    "val", [datetime.datetime(2020, 1, 1), datetime.timedelta(1), [1], {1: 1}]
+)
+def test_from_py_notimplemented(val):
+    with pytest.raises(NotImplementedError):
+        plc.Scalar.from_py(val)
+
+
+@pytest.mark.parametrize("val", [object, None])
+def test_from_py_typeerror(val):
+    with pytest.raises(TypeError):
+        plc.Scalar.from_py(val)