From a04647e4a6e2a02dc5bb2baa1906555bbfde8f33 Mon Sep 17 00:00:00 2001
From: Sheilah <kirui.sheilah@gmail.com>
Date: Wed, 15 Dec 2021 19:08:47 -0800
Subject: [PATCH] converted _make_copy_replacing_NaT_with_null() into a free
 function

---
 python/cudf/cudf/core/column/column.py | 48 +++++++++++++-------------
 1 file changed, 24 insertions(+), 24 deletions(-)

diff --git a/python/cudf/cudf/core/column/column.py b/python/cudf/cudf/core/column/column.py
index 857d181fb22..a3a8b0c91d1 100644
--- a/python/cudf/cudf/core/column/column.py
+++ b/python/cudf/cudf/core/column/column.py
@@ -306,25 +306,6 @@ def _get_mask_as_column(self) -> ColumnBase:
             self.base_mask, self.offset, self.offset + len(self)
         )
 
-    def _make_copy_replacing_NaT_with_null(self):
-        """Return a copy with NaT values replaced with nulls."""
-        if np.issubdtype(self.dtype, np.timedelta64):
-            na_value = np.timedelta64("NaT", self.time_unit)
-
-        elif np.issubdtype(self.dtype, np.datetime64):
-            na_value = np.datetime64("NaT", self.time_unit)
-
-        null = column_empty_like(self, masked=True, newsize=1)
-        out_col = cudf._lib.replace.replace(
-            self,
-            build_column(
-                Buffer(np.array([na_value], dtype=self.dtype).view("|u1")),
-                dtype=self.dtype,
-            ),
-            null,
-        )
-        return out_col
-
     def memory_usage(self) -> int:
         n = 0
         if self.data is not None:
@@ -1671,6 +1652,27 @@ def build_struct_column(
     return cast("cudf.core.column.StructColumn", result)
 
 
+def _make_copy_replacing_NaT_with_null(column):
+    """Return a copy with NaT values replaced with nulls."""
+    if np.issubdtype(column.dtype, np.timedelta64):
+        na_value = np.timedelta64("NaT", column.time_unit)
+    elif np.issubdtype(column.dtype, np.datetime64):
+        na_value = np.datetime64("NaT", column.time_unit)
+    else:
+        raise ValueError("This type does not support replacing NaT with null.")
+
+    null = column_empty_like(column, masked=True, newsize=1)
+    out_col = cudf._lib.replace.replace(
+        column,
+        build_column(
+            Buffer(np.array([na_value], dtype=column.dtype).view("|u1")),
+            dtype=column.dtype,
+        ),
+        null,
+    )
+    return out_col
+
+
 def as_column(
     arbitrary: Any,
     nan_as_null: bool = None,
@@ -1772,9 +1774,7 @@ def as_column(
                 col = col.set_mask(mask)
         elif np.issubdtype(col.dtype, np.datetime64):
             if nan_as_null or (mask is None and nan_as_null is None):
-                # Ignore typing error since this method is only defined for
-                # DatetimeColumn, not the ColumnBase class.
-                col = col._make_copy_replacing_NaT_with_null()  # type: ignore
+                col = _make_copy_replacing_NaT_with_null(col)
         return col
 
     elif isinstance(arbitrary, (pa.Array, pa.ChunkedArray)):
@@ -1905,7 +1905,7 @@ def as_column(
             mask = None
             if nan_as_null is None or nan_as_null is True:
                 data = build_column(buffer, dtype=arbitrary.dtype)
-                data = data._make_copy_replacing_NaT_with_null()
+                data = _make_copy_replacing_NaT_with_null(data)
                 mask = data.mask
 
             data = cudf.core.column.datetime.DatetimeColumn(
@@ -1923,7 +1923,7 @@ def as_column(
             mask = None
             if nan_as_null is None or nan_as_null is True:
                 data = build_column(buffer, dtype=arbitrary.dtype)
-                data = data._make_copy_replacing_NaT_with_null()
+                data = _make_copy_replacing_NaT_with_null(data)
                 mask = data.mask
 
             data = cudf.core.column.timedelta.TimeDeltaColumn(