python: pl.struct allow eager eval (#3161)

py-polars/polars/internals/lazy_functions.py

@@ -1420,14 +1420,43 @@ def select(
     return pli.DataFrame([]).select(exprs)
 
 
-def struct(exprs: Union[Sequence[Union["pli.Expr", str]], "pli.Expr"]) -> "pli.Expr":
+@overload
+def struct(
+    exprs: Union[Sequence[Union["pli.Expr", str, "pli.Series"]], "pli.Expr"],
+    eager: Literal[True],
+) -> "pli.Series":
+    ...
+
+
+@overload
+def struct(
+    exprs: Union[Sequence[Union["pli.Expr", str, "pli.Series"]], "pli.Expr"],
+    eager: Literal[False],
+) -> "pli.Expr":
+    ...
+
+
+@overload
+def struct(
+    exprs: Union[Sequence[Union["pli.Expr", str, "pli.Series"]], "pli.Expr"],
+    eager: bool = False,
+) -> Union["pli.Expr", "pli.Series"]:
+    ...
+
+
+def struct(
+    exprs: Union[Sequence[Union["pli.Expr", str, "pli.Series"]], "pli.Expr"],
+    eager: bool = False,
+) -> Union["pli.Expr", "pli.Series"]:
     """
     Collect several columns into a Series of dtype Struct
 
     Parameters
     ----------
     exprs
         Columns/Expressions to collect into a Struct
+    eager
+        Evaluate immediately
 
     Examples
     --------
@@ -1473,6 +1502,9 @@ def struct(exprs: Union[Sequence[Union["pli.Expr", str]], "pli.Expr"]) -> "pli.E
     └─────┴───────┴─────┴───────────────────────────────┘
 
     """
+
+    if eager:
+        return pli.select(struct(exprs, eager=False)).to_series()
     exprs = pli.selection_to_pyexpr_list(exprs)
     return pli.wrap_expr(_as_struct(exprs))
 

py-polars/tests/test_struct.py

@@ -136,3 +136,8 @@ def test_nested_struct() -> None:
     assert isinstance(nest_l2.dtypes[0], pl.datatypes.Struct)
     assert nest_l2.dtypes[0].inner_types == nest_l1.dtypes
     assert isinstance(nest_l1.dtypes[0], pl.datatypes.Struct)
+
+
+def test_eager_struct() -> None:
+    s = pl.struct([pl.Series([1, 2, 3]), pl.Series(["a", "b", "c"])], eager=True)
+    assert s.dtype == pl.Struct