REGR: only convert at end for Block.replace_list

pandas/core/internals/blocks.py

@@ -555,6 +555,8 @@ def replace(
         to_replace,
         value,
         inplace: bool = False,
+        # conversion is done at the end if we're called from replace_list
+        convert: bool = True,
         # mask may be pre-computed if we're called from replace_list
         mask: npt.NDArray[np.bool_] | None = None,
     ) -> list[Block]:
@@ -572,6 +574,7 @@ def replace(
         if isinstance(values, Categorical):
             # TODO: avoid special-casing
             blk = self if inplace else self.copy()
+            # TODO: should we pass convert here? moot point if special casing avoided.
             blk.values._replace(to_replace=to_replace, value=value, inplace=True)
             return [blk]
 
@@ -592,7 +595,7 @@ def replace(
         elif self._can_hold_element(value):
             blk = self if inplace else self.copy()
             putmask_inplace(blk.values, mask, value)
-            if not (self.is_object and value is None):
+            if convert and not (self.is_object and value is None):
                 # if the user *explicitly* gave None, we keep None, otherwise
                 #  may downcast to NaN
                 blocks = blk.convert(numeric=False, copy=False)
@@ -606,6 +609,7 @@ def replace(
                 to_replace=to_replace,
                 value=value,
                 inplace=True,
+                convert=convert,
                 mask=mask,
             )
 
@@ -619,6 +623,7 @@ def replace(
                         to_replace=to_replace,
                         value=value,
                         inplace=True,
+                        convert=convert,
                         mask=mask[i : i + 1],
                     )
                 )
@@ -630,8 +635,10 @@ def _replace_regex(
         to_replace,
         value,
         inplace: bool = False,
+        # conversion is done at the end if we're called from replace_list
         convert: bool = True,
-        mask=None,
+        # mask may be pre-computed if we're called from replace_list
+        mask: npt.NDArray[np.bool_] | None = None,
     ) -> list[Block]:
         """
         Replace elements by the given value.
@@ -664,7 +671,10 @@ def _replace_regex(
         replace_regex(new_values, rx, value, mask)
 
         block = self.make_block(new_values)
-        return block.convert(numeric=False, copy=False)
+        if convert:
+            return block.convert(numeric=False, copy=False)
+        else:
+            return [block]
 
     @final
     def replace_list(
@@ -707,7 +717,7 @@ def replace_list(
         masks = [extract_bool_array(x) for x in masks]  # type: ignore[arg-type]
 
         rb = [self if inplace else self.copy()]
-        for i, (src, dest) in enumerate(pairs):
+        for i, (to_replace, value) in enumerate(pairs):
             convert = i == src_len  # only convert once at the end
             new_rb: list[Block] = []
 
@@ -723,8 +733,8 @@ def replace_list(
                     m = mib[blk_num : blk_num + 1]
 
                 result = blk._replace_coerce(
-                    to_replace=src,
-                    value=dest,
+                    to_replace=to_replace,
+                    value=value,
                     mask=m,
                     inplace=inplace,
                     regex=regex,
@@ -785,7 +795,11 @@ def _replace_coerce(
                 putmask_inplace(nb.values, mask, value)
                 return [nb]
             return self.replace(
-                to_replace=to_replace, value=value, inplace=inplace, mask=mask
+                to_replace=to_replace,
+                value=value,
+                inplace=inplace,
+                convert=False,
+                mask=mask,
             )
 
     # ---------------------------------------------------------------------