Make cudf._lib.string_udf work with pylibcudf Columns instead of cudf…

…._lib Columns (#17715)

With the possibility of the `cudf._lib.Column` being refactored (possibly to a pure Python implementation), this PR makes the `string_udf` routines dependent on pylibcudf instead of the the cudf classic Cython based Column

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

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

URL: #17715

python/cudf/cudf/_lib/strings_udf.pyx

@@ -1,4 +1,4 @@
-# Copyright (c) 2022-2024, NVIDIA CORPORATION.
+# Copyright (c) 2022-2025, NVIDIA CORPORATION.
 
 from libc.stdint cimport uint8_t, uint16_t, uintptr_t
 from pylibcudf.libcudf.strings_udf cimport (
@@ -25,15 +25,14 @@ from pylibcudf.libcudf.strings_udf cimport (
 from rmm.librmm.device_buffer cimport device_buffer
 from rmm.pylibrmm.device_buffer cimport DeviceBuffer
 
-from cudf._lib.column cimport Column
 from pylibcudf cimport Column as plc_Column
 
 
 def get_cuda_build_version():
     return cpp_get_cuda_build_version()
 
 
-def column_to_string_view_array(Column strings_col):
+def column_to_string_view_array(plc_Column strings_col):
     cdef unique_ptr[device_buffer] c_buffer
     cdef column_view input_view = strings_col.view()
     with nogil:
@@ -52,9 +51,7 @@ def column_from_udf_string_array(DeviceBuffer d_buffer):
         c_result = move(cpp_column_from_udf_string_array(data, size))
         cpp_free_udf_string_array(data, size)
 
-    return Column.from_pylibcudf(
-        plc_Column.from_libcudf(move(c_result))
-    )
+    return plc_Column.from_libcudf(move(c_result))
 
 
 def get_character_flags_table_ptr():

python/cudf/cudf/core/udf/utils.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2020-2024, NVIDIA CORPORATION.
+# Copyright (c) 2020-2025, NVIDIA CORPORATION.
 from __future__ import annotations
 
 import functools
@@ -20,6 +20,7 @@
 import rmm
 
 from cudf._lib import strings_udf
+from cudf._lib.column import Column
 from cudf.api.types import is_scalar
 from cudf.core.column.column import as_column
 from cudf.core.dtypes import dtype
@@ -44,6 +45,11 @@
 if TYPE_CHECKING:
     from collections.abc import Callable
 
+    import pylibcudf as plc
+
+    from cudf.core.buffer.buffer import Buffer
+    from cudf.core.indexed_frame import IndexedFrame
+
 # Maximum size of a string column is 2 GiB
 _STRINGS_UDF_DEFAULT_HEAP_SIZE = os.environ.get("STRINGS_UDF_HEAP_SIZE", 2**31)
 _heap_size = 0
@@ -298,12 +304,14 @@ def _get_kernel(kernel_string, globals_, sig, func):
     return kernel
 
 
-def _get_input_args_from_frame(fr):
-    args = []
+def _get_input_args_from_frame(fr: IndexedFrame) -> list:
+    args: list[Buffer | tuple[Buffer, Buffer]] = []
     offsets = []
     for col in _supported_cols_from_frame(fr).values():
         if col.dtype == _cudf_str_dtype:
-            data = column_to_string_view_array_init_heap(col)
+            data = column_to_string_view_array_init_heap(
+                col.to_pylibcudf(mode="read")
+            )
         else:
             data = col.data
         if col.mask is not None:
@@ -325,7 +333,9 @@ def _return_arr_from_dtype(dtype, size):
 
 def _post_process_output_col(col, retty):
     if retty == _cudf_str_dtype:
-        return strings_udf.column_from_udf_string_array(col)
+        return Column.from_pylibcudf(
+            strings_udf.column_from_udf_string_array(col)
+        )
     return as_column(col, retty)
 
 
@@ -365,7 +375,7 @@ def set_malloc_heap_size(size=None):
         _heap_size = size
 
 
-def column_to_string_view_array_init_heap(col):
+def column_to_string_view_array_init_heap(col: plc.Column) -> Buffer:
     # lazily allocate heap only when a string needs to be returned
     return strings_udf.column_to_string_view_array(col)
 

python/cudf/cudf/tests/test_string_udfs.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2022-2024, NVIDIA CORPORATION.
+# Copyright (c) 2022-2025, NVIDIA CORPORATION.
 
 import numba
 import numpy as np
@@ -11,6 +11,7 @@
 import rmm
 
 import cudf
+from cudf._lib.column import Column
 from cudf._lib.strings_udf import (
     column_from_udf_string_array,
     column_to_string_view_array,
@@ -87,14 +88,16 @@ def run_udf_test(data, func, dtype):
         )
 
     cudf_column = cudf.core.column.as_column(data)
-    str_views = column_to_string_view_array(cudf_column)
+    str_views = column_to_string_view_array(
+        cudf_column.to_pylibcudf(mode="read")
+    )
     sv_kernel, udf_str_kernel = get_kernels(func, dtype, len(data))
 
     expect = pd.Series(data).apply(func)
     with _CUDFNumbaConfig():
         sv_kernel.forall(len(data))(str_views, output)
     if dtype == "str":
-        result = column_from_udf_string_array(output)
+        result = Column.from_pylibcudf(column_from_udf_string_array(output))
     else:
         result = output
 
@@ -103,7 +106,7 @@ def run_udf_test(data, func, dtype):
     with _CUDFNumbaConfig():
         udf_str_kernel.forall(len(data))(str_views, output)
     if dtype == "str":
-        result = column_from_udf_string_array(output)
+        result = Column.from_pylibcudf(column_from_udf_string_array(output))
     else:
         result = output