Return head

py-polars/polars/_utils/various.py

@@ -629,3 +629,10 @@ def re_escape(s: str) -> str:
     # escapes _only_ those metachars with meaning to the rust regex crate
     re_rust_metachars = r"\\?()|\[\]{}^$#&~.+*-"
     return re.sub(f"([{re_rust_metachars}])", r"\\\1", s)
+
+
+def try_head(seq: Sequence[Any] | Any, default: Any) -> Any:
+    try:
+        return seq[0]
+    except TypeError:
+        return default

py-polars/polars/lazyframe/frame.py

@@ -45,6 +45,7 @@
     issue_warning,
     normalize_filepath,
     parse_percentiles,
+    try_head,
 )
 from polars._utils.wrap import wrap_df, wrap_expr
 from polars.datatypes import (
@@ -1370,18 +1371,8 @@ def sort(
         """
         # Fast path for sorting by a single existing column
         if isinstance(by, str) and not more_by:
-            if (isinstance(descending, list) and len(descending) != 1) or (
-                isinstance(nulls_last, list) and len(nulls_last) != 1
-            ):
-                msg = (
-                    "size of `descending` or `nulls_last` "
-                    "must be 1 when defined as list"
-                )
-                raise ValueError(msg)
-            if isinstance(descending, list):
-                descending = descending[0]
-            if isinstance(nulls_last, list):
-                nulls_last = nulls_last[0]
+            descending = try_head(descending, descending)
+            nulls_last = try_head(nulls_last, nulls_last)
             return self._from_pyldf(
                 self._ldf.sort(
                     by, descending, nulls_last, maintain_order, multithreaded

py-polars/tests/unit/dataframe/test_df.py

@@ -362,18 +362,6 @@ def test_sort_multi_output_exprs_01() -> None:
     ):
         df.sort("dts", "strs", nulls_last=[True, False, True])
 
-    with pytest.raises(
-        ValueError,
-        match="size of `descending` or `nulls_last` must be 1 when defined as list",
-    ):
-        df.sort(by="dts", descending=[True, False])
-
-    with pytest.raises(
-        ValueError,
-        match="size of `descending` or `nulls_last` must be 1 when defined as list",
-    ):
-        df.sort(by="dts", nulls_last=[True, False])
-
     # No columns selected - return original input.
     assert_frame_equal(df, df.sort(pl.col("^xxx$")))